hwc: Add support for uneven split primary displays

Add support for unevenly split primary displays.
The driver provides info about the split via msm_fb_split sysfs node

For external we assume even split. If driver doesn't specify any split
for primary, we default to even split.

Change-Id: I4d541f41de2d7a5d2b62653fa33cab079a6d5d30
8 files changed