MIPS: Netlogic: Update PIC access functions

Remove unused and trivial PIC accesss functions, update nlm_pic_send_ipi()
and nlm_set_irt_to_cpu() to use similar logic, and use correct type for
reg in nlm_pic_disable_irt().

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Patchwork: http://patchwork.linux-mips.org/patch/4463


Signed-off-by: John Crispin <blogic@openwrt.org>