Fix for HW CRC calculations on Silicon Labs targets

[stevew817]

Description

Fixes the issue discovered in #8011. In short, 32-bit writes to the hardware CRC engine can only happen for a 32-bit polynomial. The reason this had not been discovered earlier is that the tests, when compiled with a release profile (which is the default) are likely to have non-aligned strings, which caused the CRC input code to go into byte-per-byte copy mode and never exercise the word-copy mode.

Verified by running both tests-mbed_hal-crc and tests-mbed_drivers-crc on both a release and debug profile.

Pull request type

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

[0xc0170]

cc @studavekar

[kjbracey]

Looks correct, just nit-picking on style.

[stevew817]

@kjbracey-arm I applied changes according to your style comments. Can we get this fix in?

[cmonr]

/moprh build

[stevew817]

@cmonr typo? :)

[cmonr]

Typo...

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3135
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8026/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2743
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8026/

[mbed-ci]

Test : SUCCESS

Build number : 2940
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8026/2940