msm: mdss: change MDP burst length to 16 on 8x10

Display DMA bus master is a real time client, which
means it has strict timing requirement to meet the
panel timing.   If the data cannot be fetched from
memory and sent to the panel fast enough within the
panel timing constraint, the MDP DMA engine will be
starving and cause under-run.  Earlier, we were using
burst length 8, this burst length configuration will
cause under-run on the 720p panel which has high bandwidth
requirement compared to WVGA panel.  The burst length
is now increased to 16.

Change-Id: I1de8e453fa5d99634b6c0ab38ed8568c91516001
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>