mb/google/guybrush/dewatt: Add variant to disable HDMI

For one specific type of APU, it doesn't have HDMI. When we detect
this APU, we need to explicitly disable HDMI in DDI settings,
otherwise the system would freeze.

get_cpu_count() == 4 && get_threads_per_core() == 2: This case is for
2 Core and 4 Thread CPU (2C/4T for short).
get_cpu_count() == 2: This is for 2C/2T. This is for a possible future case.

BUG=b:208677293

Change-Id: I8d0fa96818a768b7960d92821b927dbc622675ae
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61260
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Chris Wang <chris.wang@amd.corp-partner.google.com>

src/mainboard/google/guybrush/variants/dewatt/Makefile.inc

@@ -6,3 +6,5 @@ ramstage-y += gpio.c
 verstage-y += gpio.c
 
 subdirs-y += ./memory
+
+romstage-y += variant.c

src/mainboard/google/guybrush/variants/dewatt/variant.c

@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <baseboard/variants.h>
+#include <amdblocks/cpu.h>
+
+void variant_update_ddi_descriptors(fsp_ddi_descriptor *ddi_descriptors)
+{
+	if ((get_cpu_count() == 4 && get_threads_per_core() == 2) || get_cpu_count() == 2)
+		ddi_descriptors[1].connector_type = DDI_UNUSED_TYPE;
+}