iommu/arm-smmu: Switch to subsys_initcall for driver registration

This should ensure that arm-smmu is initialized before other drivers
start handling devices that propably need smmu support.

Change-Id: Ieaf573244df9db97ab794cc66d03d85b1c75fa6e
Signed-off-by: Andreas Herrmann <andreas.herrmann@calxeda.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: b1950b2796da80b66df02db39cc3417266b73767
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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