arm64: dma-mapping: remove order parameter from arm_iommu_create_mapping()

arm32 recently removed the `order' parameter from
arm_iommu_create_mapping: (68efd7d2: arm: dma-mapping: remove order
parameter from arm_iommu_create_mapping()) in order to make the API
easier to understand.  The arm32 DMA IOMMU mapper has dynamic resizing
of the iova bitmap, so there was no reason to keep the `order' parameter
around (which was introduced to reduce the size of the bitmap).

Although we don't have dynamic iova bitmap reallocation on arm64, we'd
still like to get rid of the `order' parameter since it's confusing and
doesn't really help much (especially since all known clients on our
system are passing order=0).  Remove it.

Change-Id: I35e32fdfbe05ec434f64a3a316d13c8f43304bc6
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>