hwc: Get the retire fence from the MDP driver

Get the retire fence separately instead of duplicating the
release fence.

Bug: 9319776
Signed-off-by: Iliyan Malchev <malchev@google.com>

Conflicts:
	common.mk
Change-Id: Iacb773c2d94f635e27a7b355d399cb2e36dac2a5