drm/i915/bios: Define VBT block 20 (OEM Customizable Modes) contents

Define the contents of VBT block 20 (OEM Customizable Modes).
Each entry is either 26 or 28 bytes, depending on the BDB version.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240503122449.27266-22-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -897,6 +897,30 @@ struct bdb_display_remove_old {
 	struct display_remove_entry_old table[];
 } __packed;
 
+/*
+ * Block 20 - OEM Customizable Modes
+ */
+
+struct oem_mode {
+	u8 enable_in_vbios:1;
+	u8 enable_in_os:1;
+	u8 enable_in_gop:1;					/* 207+ */
+	u8 reserved:5;
+	u8 display_flags;					/* ???-216 */
+	u16 x_res;
+	u16 y_res;
+	u8 color_depth;
+	u8 refresh_rate;
+	struct bdb_edid_dtd dtd;
+	u16 display_flags_2;					/* 217+ */
+} __packed;
+
+struct bdb_oem_custom {
+	u8 num_entries;
+	u8 entry_size;
+	struct oem_mode modes[];
+} __packed;
+
 /*
  * Block 22 - SDVO LVDS General Options
  */