drm/i915/display: Add definition for MCURSOR_MODE_64_2B

MCURSOR_MODE_64_2B is used in Wa_16021440873. Add define for it.

Bspec: 69837

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240319123327.1661097-5-jouni.hogander@intel.com