drm/i915/dsi/xelpd: Add WA to program LP to HS wakeup guardband

Wa_16012360555 SW will have to program the "LP to HS Wakeup Guardband"
field to account for the repeaters on the HS Request/Ready PPI signaling
between the Display engine and the DPHY.

v2: Fix build issue.
v3: Align to new naming (Jani)

Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210826054811.10572-2-vandita.kulkarni@intel.com