iommu/arm-smmu: Convert GR1 registers to bitfields

As for GR0, use the bitfield helpers to make GR1 usage a little cleaner,
and use it as an opportunity to audit and tidy the definitions. This
tweaks the handling of CBAR types to match what we did for S2CR a while
back, and fixes a couple of names which didn't quite match the latest
architecture spec (IHI0062D.c).

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>