drm/i915/psr: Nuke aux frame sync

eDP spec states that aux frame is required to do PSR2 selective
update but i915 don't fully implement it. It sends the aux frame
sync messages but the value is always zero as the GTC is not enabled
in driver.

Through tests was findout that pannels can do selective update when
the y-coordinate is also included in SDP, that is why it is required
to run PSR2 in i915.

A dummy value is not useful at all to sink, so removing everything
related to aux frame sync, if GTC is enabled we can bring this back.

Cc: Vathsala Nagaraju <vathsala.nagaraju@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180328223046.16125-3-jose.souza@intel.com