drm/i915/icl: update VBT's child_device_config flags2 field

Some bits from the flags2 field are going to be used in the next
patches, so replace the whole-byte definition with the actual bits and
document their versions.

This patch is based on a patch by Animesh Manna.

Cc: Animesh Manna <animesh.manna@intel.com>
Credits-to: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180614221018.19044-2-paulo.r.zanoni@intel.com

drivers/gpu/drm/i915/intel_vbt_defs.h

@@ -420,7 +420,9 @@ struct child_device_config {
 	u16 extended_type;
 	u8 dvo_function;
 	u8 dp_usb_type_c:1;					/* 195 */
-	u8 flags2_reserved:7;					/* 195 */
+	u8 tbt:1;						/* 209 */
+	u8 flags2_reserved:2;					/* 195 */
+	u8 dp_port_trace_length:4;				/* 209 */
 	u8 dp_gpio_index;					/* 195 */
 	u16 dp_gpio_pin_num;					/* 195 */
 	u8 dp_iboost_level:4;					/* 196 */