Linker files for LPC11U68 and LPC1549 updated

[deepikabhavnani]

Description

Update linker files and resolve build issue
Linker files for LPC11U68 and LPC1549 updated as Mbed OS memory model

1. LPC1549 - Has multiple memory banks, 4K bank used for stack exclusively and 16K for Heap. Its is mbed 2 only target hence 4K for stack.
2. LPC11U68 - Added Heap and Stack sections in linker files. Resolved build issues.

Dependent on : #9571

Pull request type

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

Reviewers

@mmahadevan108 @mprse

Targeted for Minor release - As dependent on #9571

[ciarmcom]

@deepikabhavnani, thank you for your changes.
@mprse @ARMmbed/mbed-os-maintainers please review.

[mprse]

Looks good!

[0xc0170]

why are we adding this macro?

[deepikabhavnani]

As part of linker file updates #9571, it was discovered that these 2 targets needed additional fixes. Hence separate PR was created.

LPC11U68 had build issues - to resolve that Stack and heap section was added to linker file and MBED_FAULT_HANDLER_DISABLED was disabled.

Issues were communicated and resolved over mail with NXP.

[deepikabhavnani]

If this PR is approved, I can cherry-pick commits and apply them on #9571, if approval for 9571 takes more than a week

[cmonr]

#9667 (comment)

Let's move forward with that, since this PR feels ready.

[cmonr]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 12 of 12 test jobs passed
Build number : 1
Build artifacts

[deepikabhavnani]

@ARMmbed/mbed-os-maintainers - We can merge this PR, this PR is in line to changes of other PR (not directly dependent). We just need to be sure that both of them are for minor release.