drm/vc4: kms: Fix VBLANK reporting on a disabled CRTC

drm/vc4: kms: Fix VBLANK reporting on a disabled CRTC

If a CRTC is enabled but not active, and that we're then doing a page flip
on another CRTC, drm_atomic_get_crtc_state will bring the first CRTC state
into the global state, and will make us wait for its vblank as well, even
though that might never occur.

Fix this by considering all the enabled CRTCs by either using their new
state in the global state, or using their current state if they aren't part
of the new state being checked, to remove their assigned channel from the
pool before started to assign channels to CRTCs enabled by the state.

Fixes: 87ebcd42fb7b ("drm/vc4: crtc: Assign output to channel automatically")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
[hoegeun.kwon: Needed to fix page flip issue of dual hdmi.]
Signed-off-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Change-Id: Ic8b8083a652df142a17ec0d50f6c2572494ba3c0