msm: camera: fd: Attach iommu dynamically

When iommu device is attached, iommu
framework will keep the regulator enabled.

We should not attach iommu if buffers are not
used. Move attach iommu from open to map
buffers, and detach iommu from release to
unmap buffers.

Change-Id: Ifdf56bd43f1e1f3b9077c6879063bc61b5b7d929
Signed-off-by: Gjorgji Rosikopulos <grosik@codeaurora.org>