disp: msm: update seamless check for connector

During CWB case where writeback connector is disabled
and connectors_changed is set, add support to allow
disabling of corresponding encoder for this connector.
Modify the seamless check for connector to handle
the same. With this cwb + dfps concurrency can
be handled.

Change-Id: Ia8f86bd12ac3c5ab622334fb04cdcb2e2b60f111
Signed-off-by: Krishna Manikandan <mkrishn@codeaurora.org>