fix(Build): Link with libphy_hard.a when MFLOAT_ABI = hard

[khpeterson]

Pull Request Template

Description

BLE builds fail when MFLOAT_ABI = hard, e.g. with macOS 12.6.7:

khp@Kevins-MacBook-Pro-M1 BLE_periph_20230718 % make all VERBOSE=1 BOARD=FTHR PROJECT=BLE_periph_20230718 TARGET=MAX32665 MFLOAT_ABI=hard
.
.
.
arm-none-eabi-gcc @/Users/khp/Dropbox/Projects/Documents/MXC/Examples/BLE_periph_20230718/build/ln_args.txt
/usr/local/gcc-arm-none-eabi-9-2020-q2-update/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/ld: error: /Users/khp/Dropbox/Projects/Documents/MXC/Examples/BLE_periph_20230718/build/BLE_periph_20230718.elf uses VFP register arguments, /Users/khp/Dropbox/Projects/Documents/MXC/Examples/msdk/Libraries/BlePhy/MAX32665/libphy.a(pal_bb.o) does not

Changed libs.mk to select libphy_hard.a when appropriate.

Checklist Before Requesting Review

• PR Title follows correct guidelines.
• Description of changes and all other relevant information.
• (Optional) Link any related Github issues using a keyword
• (Optional) Provide info on any relevant functional testing/validation. For API changes or significant features, this is not optional.

[Jake-Carter]

Thank you @khpeterson, I appreciate the PR. Good catch on this.

I've added some hardfp tests to our build checker (7ab2e87) which should help this from slipping through again.