armclang: Fix building cortex-m4 w/o floating point

When we build for a SoC that has a cortex-m4 w/o a FPU that
utilizes CMSIS headers with armclang (like mec1501modular_assy6885)
we get the following warning:

modules/hal/cmsis/CMSIS/Core/Include/core_cm4.h:93:8: warning:
   "Compiler generates FPU instructions for a device without
    an FPU (check __FPU_PRESENT)" [-W#warnings]
   #warning "Compiler generates FPU instructions for a device
   without an FPU (check __FPU_PRESENT)"

Fix the by setting -mfloat-abi=soft for such cases that don't have FPU
enabled.

Fixes #56068

Signed-off-by: Kumar Gala <kumar.gala@intel.com>
(cherry picked from commit 32a48f2f)