drm/i915/display: extract code to prepare qgv points mask

Extract the code to prepare the QGV points mask as per the
format expected by the pcode as this could be utlized from
multiple points.

Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240405113533.338553-4-vinod.govindapillai@intel.com