drm/i915/display: Unify VSC SPD preparation

There is no specific reason to prepare VSC SDP for PSR case somehow
differently. Unify PSR and non-PSR preparation.

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Tested-by: Shawn Lee <shawn.c.lee@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231220103609.1384523-4-jouni.hogander@intel.com