MIPS: IP27: Update/restructure CPU overrides

Inspired by Maciej's recent patch to update DEC cpu-feature-overrides.h,
I updated IP27's as well to disable features known to not apply to the
IP27 platform or the R10K-series of CPUs.

Before:
   text    data     bss     dec     hex filename
8616648  463200  472240 9552088  91c0d8 vmlinux

After:
   text    data     bss     dec     hex filename
8592256  471392  472240 9535888  918190 vmlinux

I believe the increase in the size of the data section is for the same
reasons as in the DEC patch.

Signed-off-by: Joshua Kinard <kumba@gentoo.org>
Cc: linux-mips@linux-mips.org
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>