drm/i915/psr: Fix for Panel Replay X granularity DPCD register handling

drm/i915/psr: Fix for Panel Replay X granularity DPCD register handling

DP specification is saying value 0xff 0xff in PANEL REPLAY SELECTIVE UPDATE
X GRANULARITY CAPABILITY registers (0xb2 and 0xb3) means full-line
granularity. Take this into account when handling Panel Replay X
granularity informed by the panel.

Fixes: 1cc854647450 ("drm/i915/psr: Use SU granularity information available in intel_connector")
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7284
Tested-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patch.msgid.link/20260225074221.1744330-2-jouni.hogander@intel.com