iommu/arm-smmu: clean up use of `flags' in page table handling code

Commit 972157cac528 ("arm/smmu: Use irqsafe spinlock for domain lock")
fixed our page table locks to be the irq{save,restore} variants, since
the DMA mapping API can be invoked from interrupt context.

This patch cleans up our use of the flags variable so we can distinguish
between IRQ flags (now `flags') and pte protection bits (now `prot').

Change-Id: I2c505f19193c110f4477fa9aeb8f51ad168a818b
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: b410aed93288d0bd7650c4d17fd0f306b5082d6f
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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