hwc: Use max pipe width instead of max mixer width for splitting

Not necessarily the max width supported by the MDP pipe and mixer
need to be same. HWC has to make the decision for using one OR
two pipes per layer only based on the max width supported by the
pipe not the mixer.

Change-Id: I5a2495d07de1b6f54ef64d9140c909f0f4cef914
8 files changed