drm/i915/bios: Add the old DPST field into VBT LFP power block

According to some VBIOS sources the LFP power block used to
have a single bit for DPST support. In version 159 that bit
got moved into the driver features block, and then in version
228 back into the LFP power block (but this time as a
per-panel thing). We have definitions for the last two, but
not the original bit. Define it as well.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240321161806.31714-4-ville.syrjala@linux.intel.comAcked-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_vbt_defs.h

@@ -918,7 +918,7 @@ struct bdb_lfp_backlight_data {
  * Block 44 - LFP Power Conservation Features Block
  */
 struct lfp_power_features {
-	u8 reserved1:1;
+	u8 dpst_support:1;						/* ???-159 */
 	u8 power_conservation_pref:3;
 	u8 reserved2:1;
 	u8 lace_enabled_status:1;					/* 210+ */