disp: msm: sde: use new state when checking conn-crtc association

Currently during CRTC atomic check phase, driver is counting
the number of connectors attached to the CRTC by iterating over
all the connectors available and checking if they are attached
to the CRTC. The current implementation uses the old connector
state, which has an invalid state for the first commit. This
causes the number of attached connectors to always be 0 for the
first commit.

This change extracts the new connector state from the atomic state
and ensures the calculation is done before checking crtc features.

Change-Id: I58d641086f18e8624cbc2d432443323a6a44792e
Signed-off-by: Amine Najahi <anajahi@codeaurora.org>