arch: arm: Add unified floating-point configuration symbols

This commit adds the unified floating-point configuration symbols for
the ARM architectures.

These configuration symbols allow specification of the floating-point
coprocessors, such as VFP (also known as FP for Cortex-M) and NEON,
for the ARM architectures.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>