MIPS: mipsregs.h: Remove broken comments

Remove a duplicate FPU Status Register reference that has been there
since forever and a mistakenly copied and pasted R4xx0 manual reference.

[ralf@linux-mips.org: Fix conflict.]

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9666/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>