msm: mdss: use DMA_BIDIRECTIONAL for 8937

Simultaneous buffer maps with read and write permissions are
possible due to the asynchronous nature of MDSS driver.

Client stages the same buffer on MDP & ROTATOR. It calls the map
API for both at the same time. Due to concurrency, the source buffer
is mapped by MDP before and is ref-counted. ROTATOR API called later never
updates the permission which is required for dst buffer.
This leads to permission fault. Requesting the map with DMA_BIDIRECTIONAL
flag to fix the issue.

Change-Id: Ieb819820b19d163fee541dd571c5a58dc78be7d3
Signed-off-by: Kalyan Thota <kalyant@codeaurora.org>