drm/i915/fbc: Reallocate cfb if we need more of it

drm/i915/fbc: Reallocate cfb if we need more of it

The code assumes we can omit the cfb allocation once fbc
has been enabled once. That's nonsense. Let's try to
reallocate it if we need to.

The code is still a mess, but maybe this is enough to get
fbc going in some cases where it initially underallocates
the cfb and there's no full modeset to fix it up.

Cc: Daniel Drake <drake@endlessm.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Jian-Hong Pan <jian-hong@endlessm.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191127201222.16669-15-ville.syrjala@linux.intel.com
Tested-by: Daniel Drake <drake@endlessm.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>