MIPS: Correct `nofpu' non-functionality

The `cpu_has_fpu' feature flag must not be hardcoded to 1 or the `nofpu'
kernel option will be ignored.  Remove any such overrides and add a
cautionary note.  Hardcoding to 0 is fine for FPU-less platforms.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9694/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>