mb/google/dedede: Add a variant callback to update devicetree config

This callback is required to update the devicetree config at run-time
after probing the firmware config.

BUG=b:186380807
BRANCH=dedede
TEST=Build and boot to OS in metaknight.

Change-Id: I857211bfc4beb36ab225f3786c1707336a34aae9
Signed-off-by: David Wu <david_wu@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52887
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Raymond Wong <wongraymond@google.com>

src/mainboard/google/dedede/mainboard.c

@@ -40,10 +40,17 @@ static void mainboard_init(void *chip_info)
 	gpio_configure_pads_with_override(base_pads, base_num,
 		override_pads, override_num);
 
+	variant_devtree_update();
+
 	if (CONFIG(BOARD_GOOGLE_BASEBOARD_DEDEDE_CR50))
 		mainboard_update_soc_chip_config();
 }
 
+void __weak variant_devtree_update(void)
+{
+	/* Override dev tree settings per board */
+}
+
 static void mainboard_dev_init(struct device *dev)
 {
 	mainboard_ec_init();

src/mainboard/google/dedede/variants/baseboard/include/baseboard/variants.h

@@ -39,4 +39,7 @@ bool variant_mem_is_half_populated(void);
 /* Allow each variants to customize SMI sleep flow. */
 void variant_smi_sleep(u8 slp_typ);
 
+/* Modify devictree settings during ramstage. */
+void variant_devtree_update(void);
+
 #endif /*__BASEBOARD_VARIANTS_H__ */