arm64: pgtable: use pte_index instead of __pte_index

pte_index is a useful helper outside of arch/arm64, for things like the
ARM SMMU driver, so rename __pte_index to pte_index to be consistent
with both arch/arm/ and also the definitions of pmd_index and pgd_index.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-commit: 9ab6d02fddc6831b166812956ff387d7112ff626
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>