arm: mm: add check for coherency in arm_iommu_free_attrs

Some users pass DMA_ATTR_FORCE_COHERENT for per buffer coherency in
which case kernel uses the normal instead of coherent iommu ops. As
with the current implementation, while allocation returns normal memory
and freeing happens treating it as a coherent memory causing the below
stack. Fix it.
[<c0208d98>] __dma_free_buffer+0x34/0x44
[<c0118804>] __arm_iommu_free_attrs+0x68/0x12c
[<c0116394>] arm_iommu_free_attrs+0x64/0x6c
[<c01166a0>] dwc3_msm_gsi_ep_op+0x10e8/0x1d9c
[<c06d2860>] usb_gsi_ep_op+0x38/0x44

This fixes aebd6fce("dma-mapping: add i/o coherency support for
32bit").

Change-Id: Ic92973171f08790ecfc5345bbf7f9bc2d6606bfe
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>