CHROMIUM: WAR: misc: fastrpc: add mmap/unmap support

the client might need to request the mapping of addtional memory to
the DSP at runtime.

BUG=b:137202421
TEST=Run label_image in loop

Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Abhinav Asati <asatiabhi@codeaurora.org>
(cherry picked from commit f7dc847bd446732563327aaab962ee9ec909d813
https://github.com/ldts/qualcomm-lt-kernel/commits/chromiumos-4.14-iommu-mmap-gw-rebased-for-next

)
Change-Id: Ib029c606b6e1cd4c7fbed78e549a496721d94ba4
Signed-off-by: Vamsi Singamsetty <vamssi@codeaurora.org>