hwc: Isolate DMA state to per Display

Paddinground due to DMA state changing is modified
for the following scenarios:
Ex:  Primary + External
1.Lets say primary has the DMA pipe and DMA state is changed from
  line to Block mode then we need not invoke paddinground for External.
2.If one the displays has DMA pipe and the other
  display needs it then paddinground is invoked on both.

Change-Id: I8cb3d8138b6dfa9bef52c89e9b22616b63f4c5e4
5 files changed