msm: video: wfd: Move domain specific mappings into subdevices

Move the domain specific mappings into subdevices to abstract away iommu
from wfd-ioctl.c.  This is especially needed as the encoder subdevices
for MSM8x60 and MSM8x74 differ in the iommu domain to which they map the
buffer to.  This target specific handling needs to taken care of by the
respective subdevices rather than by wfd-ioctl which should be target
agnostic.

Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>

Conflicts:

	drivers/media/video/msm_wfd/mdp-4-subdev.c
Change-Id: I83b2cbcff2b86b0f9cce9844b1e3b1607f5881ca
Signed-off-by: Neha Pandey <nehap@codeaurora.org>