Remove the irq save/restore from write_c0_eimr(), as it is always called
with interrupts off.

This allows us to remove workaround in write_c0_eimr() to fix up the
flags used by local_irq_save. This fixup worked on XLR, but will break
when 32-bit support is added to r2 cpus like XLP.
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Patchwork: http://patchwork.linux-mips.org/patch/5022/Acked-by: John Crispin <blogic@openwrt.org>