-ffp-mode=full no longer necessary for CMSIS-DSP

Last year, -ffp-mode=full was added to the CMSIS-DSP CMake to avoid undefined behaviour due to use of INFINITY:

https://discuss.mlplatform.org/t/tensorflow-build-failure-with-arm-compiler-6-22/287

Around the same time, the INFINITYs were removed from CMSIS-DSP:

https://github.com/ARM-software/CMSIS-DSP/commit/4189b5986ced8326f146b3e2fa6451699e26762a

Now that the MLEK is using v1.16.2 of CMSIS-DSP, it no longer needs the -ffp-mode=full, so you can get some performance back.

(I haven't checked whether it's still needed for TensorFlow; I assume so).