msm-camera: Enable proportional slicing of unified buffer

Proportional slicing of unified buffer among write masters
allocates latency buffer proportional to image size each
write master is writing. This reduces image master bus
overflows

Change-Id: I8a21c8808085f527b9536edc51ccdcfa1de4e179
Signed-off-by: Mohit Setia <msetia@codeaurora.org>