drm/i915/xelpd: Handle PSR2 SDP indication in the prior scanline

drm/i915/xelpd: Handle PSR2 SDP indication in the prior scanline

In some modes there is not enough time during hblank to transmit PSR2
SDP plus the pixels CRC SDP, if such case happens PSR2 needs to be
disabled.
But eDP spec 1.4b allows to transmit PSR2 SDP in a prior scanline
alone and than later the CRC SDP, allowing PSR2 to be enabled in
those hblank constrained modes.

BSpec: 49274
Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210616203158.118111-4-jose.souza@intel.com