Instead of directly dealing with the GICH_MISR bits, move the code to
its own function and use a couple of public flags to represent the
actual state.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>