ITE: enable CPU_HAS_FPU for IT8xxx2

This option was previously enabled only if the M extension was
available, because typical compilers do not provide internal libraries
for RV32IAFC so builds fail at link-time. An appropriately-configured
compiler (such as GCC configured with
`--with-multilib-generator=rv32iac-ilp32--f`) can support such a build
however, so don't lie about the presence of an FPU.

This doesn't affect existing builds because CONFIG_FPU gates use of the
FPU, and is off by default. Enabling CONFIG_FPU will require an
appropriately-configured compiler, possibly also requiring careful
choice of CONFIG_FLOAT_HARD.

Signed-off-by: Peter Marheine <pmarheine@chromium.org>