arm/smmu: Use irqsafe spinlock for domain lock

As the lock might be used through DMA-API which is allowed
in interrupt context.

Change-Id: I4b8752a74591856a72812ff666111b904c35d13b
Signed-off-by: Joerg Roedel <joro@8bytes.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Git-commit: 972157cac528f6cfd1f7e640139287951066106e
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>