disp: msm: sde: add support for new dspp flush

SDE HW from lahaina has moved the DSPP flush bits from CTL_FLUSH
to new CTL_DSPP_x_FLUSH registers. This change brings in
support for programming the new DSPP flush registers which
allow more fine-grained control over what sub-blocks within
each DSPP get flushed.

Change-Id: Ie16c9b153d607bd7627ba02480813ab588bbe2ea
Signed-off-by: Prabhanjan Kandula <pkandula@codeaurora.org>
Signed-off-by: Steve Cohen <cohens@codeaurora.org>