drm/i915/psr: Add continuous full frame bit together with single

Currently we are observing occasionally display flickering or complete
freeze. This is narrowed down to be caused by single full frame update
(SFF).

SFF bit after it's written gets cleared by HW in subsequent vblank
i.e. when the update is sent to the panel. SFF bit is required to be
written together with partial frame update (PFU) bit. After the SFF
bit gets cleared by the HW psr2 man trk ctl register still contains
PFU bit. If there is subsequent update for any reason we will end up
having selective update/fetch configuration where start line is 0 and
end line is 0. Also selective fetch configuration for the planes is
not properly performed. This seems to be causing problems with some
panels.

Using CFF without SFF doesn't work either because it may happen that
psr2 man track ctl register is overwritten by next update before
vblank triggers sending the update. This is causing problems to
psr_invalidate/flush. Using CFF and SFF together solves the problems
as SFF is cleared only by HW in subsequent vblank and the update gets
sent.

Fix the flickering/freeze issue by keeping CFF bit as set when PSR2 is
enabled unless there is a properly configured selective update via
atomic commit.

v2:
 - Improve commit message and comments
 - No functional changes

This is also workaround for HSD 14014971508

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Mika Kahola <mika.kahola@intel.com>

Reported-by: Lee Shawn C <shawn.c.lee@intel.com>
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Tested-by: Lee Shawn C <shawn.c.lee@intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221201072308.1905679-1-jouni.hogander@intel.com