msm-camera: Divide unified buffer in proportion to the image size

Write masters writing large images require large latency buffers share
in unified buffer whereas write masters writing smaller images don't.
Allocate latency buffer in proportion to image size will reduce
image master bus overflows

Change-Id: I54d3b4389eb616b9684d5b62caaed029c83299ab
Signed-off-by: Mohit Setia <msetia@codeaurora.org>