drm/msm/sde: concurrent writeback support

Add support for capturing frame on primary through WB using
concurrent writeback HW feature if supported. Changes include
detecting CWB usecase by finding if WB is in clone mode, reserve
same set of hw resources as in plain WB case and program CWB
specific registers like ctrl_top and flush on primary. This change
support dynamic capture enable or disable per frame. Signal only
retire fence for CWB case as primary crtc handles release fence.
WB irq handling is improved using helper functions in virtual encoder.
Change also supports notifying frame error by registering for ping-pong
overflow & signal retire fence with frame error if overflows.

Change-Id: Ia9eebd0224282e87a758e848eb4e1d4ca7871059
Signed-off-by: Prabhanjan Kandula <pkandula@codeaurora.org>