MIPS: Netlogic: Remove unused EIMR/EIRR functions

Remove the definitions of {read,write}_c0_{eirr,eimr}. These functions
are now unused after the PIC and IRQ code has been updated to use
optimized EIMR/EIRR functions which work on both 32-bit and 64-bit.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Patchwork: http://patchwork.linux-mips.org/patch/5021/
Acked-by: John Crispin <blogic@openwrt.org>