TF-M config: Add max_ns_thread_count parameter

[mikisch81]

Description

#9931 reduced number of threads in block device test from 5 to 4 due to errors in TF-M targets.
The root cause of the error was the fact that TF-M had a fixed maximum number of non-secure thread allowed (defined by the TFM_MAX_NS_THREAD_COUNT in tfm_nspm.c).

This PR add a configuration parametr for this macro in mbed_lib.json and returns the number of the test to 5.

Tests results on LPC55S69:

| target            | platform_name | test suite                                                      | result | elapsed_time (sec) | copy_method |
|-------------------|---------------|-----------------------------------------------------------------|--------|--------------------|-------------|
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | OK     | 23.79              | default     |
mbedgt: test suite results: 1 OK
mbedgt: test case report:
| target            | platform_name | test suite                                                      | test case                                         | passed | failed | result | elapsed_time (sec) |
|-------------------|---------------|-----------------------------------------------------------------|---------------------------------------------------|--------|--------|--------|--------------------|
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | DEFAULT Testing get type functionality            | 1      | 0      | OK     | 0.11               |
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | FLASHIAP Testing BlockDevice erase functionality  | 1      | 0      | OK     | 0.4                |
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | FLASHIAP Testing Deinit block device              | 1      | 0      | OK     | 0.09               |
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | FLASHIAP Testing Init block device                | 1      | 0      | OK     | 0.1                |
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | FLASHIAP Testing contiguous erase, write and read | 1      | 0      | OK     | 0.12               |
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | FLASHIAP Testing multi threads erase program read | 1      | 0      | OK     | 1.3                |
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | FLASHIAP Testing program read small data sizes    | 1      | 0      | OK     | 0.13               |
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | FLASHIAP Testing read write random blocks         | 1      | 0      | OK     | 0.45               |
| LPC55S69_NS-ARMC6 | LPC55S69_NS   | mbed-os-features-storage-tests-blockdevice-general_block_device | FLASHIAP Testing unaligned erase blocks           | 1      | 0      | OK     | 0.12               |
mbedgt: test case results: 9 OK
mbedgt: completed in 24.03 sec

Pull request type

[X] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

Reviewers

@orenc17 @offirko

Release Notes

[0xc0170]

targeting 5.12.0 or later?

[mikisch81]

targeting 5.12.0 or later?

5.12.0-rc2

[offirko]

Thanks @mikisch81 - https://jira.arm.com/browse/IOTSEC-1120 , created

[offirko]

LGTM

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 13 of 13 test jobs passed
Build number : 1
Build artifacts