hwc: Set DMA state at the start of composition

* Set DMA state at the start of the composition cycle
based on the following.

Set it to LINE_MODE if the number of active rotator
sessions are 0.

Set it to BLOCK_MODE if
** A yuv-layer for any display-device requires rotation
** (or) mExtOrientation is set
** (or) mBufferMirrorMode is set

* Separate out the reset helper function into more
modular ones

Change-Id: I6a22ac4379565cd1fd2d875a7a417f4ed3ee0f1e
2 files changed