Fix USB on Kinetis devices

[c1728p9]

Description

Set correct SYSMPU register for proper USB operation. This bug was
introduced when the SYSMPU register names and defines were updated
in the commit:
"K64F: Updated the SYSMPU SDK driver"
93f8cfe

This is the same fix as #7178 but for the USB code in features/unsupported.

Pull request type

[x] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2312
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7179/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1935
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7179/

[mbed-ci]

Test : SUCCESS

Build number : 2091
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7179/2091