iommu/arm-smmu: Remove legacy bindings bus initialization initcall

No currently supported targets utilize the deprecated mmu-masters
bindings, which results in the legacy bindings initcall being a
no-op. Thus, remove the initcall to the legacy bindings routine
for now, until this can be handled properly.

Change-Id: Ie8b1004914315e757c059f8b8fc2b8713351be16
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>