mb/starlabs/starbook/rpl: Disable dynamic Tc-cold handshake

With the Tc-cold handshake, there's a fast flicker when connecting
external displays. With it disabled, it's just one "flick", so use
this as it's lesser of two evils.

Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Change-Id: Ie42b935d3e69beff6a1e503a8dee69554123b4f0
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77564
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>

src/mainboard/starlabs/starbook/variants/rpl/devicetree.cb

@@ -9,6 +9,8 @@ chip soc/intel/alderlake
 	register "cnvi_bt_core"			= "1"
 	register "cnvi_bt_audio_offload"	= "1"
 
+	register "disable_dynamic_tccold_handshake" = "1"
+
 	# Serial I/O
 	register "serial_io_i2c_mode" = "{
 		[PchSerialIoIndexI2C0]		= PchSerialIoPci,