fbdev: msm: disable cpu sync during dma_buf_map_attachment

In some usecases, the CPU_SYNC attribute is causing around
2 - 2.5ms execution time per call to dma_buf_map_attachment
while mapping the display buffers causing frame drops.
Disable CPU SYNC to resolve this.

Change-Id: I5bdf2049b265d7ed8b0a42ac92bea57296aca9f6
Signed-off-by: Nirmal Abraham <nabrah@codeaurora.org>