gic: add functions to check for and clear specific pending interrupt

Some kernel code needs to check for and clear specific pending
interrupt explicitly. The polling and clearing may happen in
contexts where interrupts are masked off at the cpu level.

Change-Id: Icba9bb2f05e9fc61dd48c4174c4d276ab20b4244
Signed-off-by: Ai Li <aili@codeaurora.org>
(cherry picked from commit 20b3c0ee6e4852af8c52fb5f98188530760c8c74)

Conflicts:

	arch/arm/include/asm/hardware/gic.h