iommu/arm-smmu: use mutex instead of spinlock for locking page tables

When creating IO mappings, we lazily allocate our page tables using the
standard, non-atomic allocator functions. This presents us with a
problem, since our page tables are protected with a spinlock.

This patch reworks the smmu_domain lock to use a mutex instead of a
spinlock. iova_to_phys is then reworked so that it only reads the page
tables, and can run in a lockless fashion, leaving the mutex to guard
against concurrent mapping threads.

Change-Id: Ib1f33fbb9c128aa48fbf91a25969144d996de3a1
Cc: <stable@vger.kernel.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: a44a9791e778d9ccda50d5534028ed4057a9a45b
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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