camera: smmu: Add support for mapping scratch buffers

Some use cases might need a scratch buffer where a virtual address
space with given length has to be mapped to a physical address space
via the smmu hardware.

So add support in the camera smmu driver to support such use cases.

Change-Id: I171232b1118acb75f7e1fc048258cd412bc9c9e2
Signed-off-by: Seemanta Dutta <seemanta@codeaurora.org>