drm/vc4: kms: Store the unassigned channel list in the state

drm/vc4: kms: Store the unassigned channel list in the state

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.

Instead of creating the list of the free channels each time atomic_check
is called, and calling drm_atomic_get_crtc_state to retrieve the
allocated channels, let's create a private state object in the main
atomic state, and use it to store the available channels.

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 and for enable
force hotplug configure. fix to unsigned long unassigned_channels instead
of integer to fix build errors.]
Signed-off-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Change-Id: Ic8bf07502f614595070e21ecc7912e671a193b09