hwc: implement smooth transition from device to client

hwc: implement smooth transition from device to client

This implementation is based on the exynos implementation

If a window with the device composition type changes a type to the client
composition type (by the e20 demands or by the driver demands) we got the
flickering as a buffer owned by this window can't be composited to the
fb_target immediately.

So we delay the unset of a hw overlay owned by this window till
the buffer get composited to the fb_target.

Change-Id: I349f752dfa71c87545f785c4eb22ce073f7cb183
Signed-off-by: Konstantin Drabeniuk <k.drabeniuk@samsung.com>