MIPS: cpu-probe: Avoid probing FPU when CONFIG_MIPS_FP_SUPPORT=n

When CONFIG_MIPS_FP_SUPPORT=n we don't support floating point so there's
no point in attempting to detect an FPU. Avoid doing so.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21021/
Cc: linux-mips@linux-mips.org