iommu/arm-smmu: Clear global and context bank fault status registers

After reset these registers have unknown values.
This might cause problems when evaluating SMMU_GFSR and/or SMMU_CB_FSR
in handlers for combined interrupts.

Change-Id: I588cd0934ec240f00bef4a5cf5f805be8ac70a04
Signed-off-by: Andreas Herrmann <andreas.herrmann@calxeda.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: 659db6f6beacae6fe49b5566debc4e82f678ff63
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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