drm/dp: Add eDP 1.5 bit definition

Add the eDP revision bit value for 1.5.

Spec: eDPv1.5 Table 16-5
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Tested-by: Ben Kao <ben.kao@intel.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250206063253.2827017-2-suraj.kandpal@intel.com