iommu/arm-smmu: Rename arm-smmu-regs.h

We're about to start using it for more than just register definitions,
so generalise the name.

Change-Id: I15630ae6f50ce8c10a624542038275861608174d
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Git-commit: c5fc6488
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>