mb/google/zork: disable eMMC per FW_CONFIG for berknip

Berknip has SSD/eMMC SKU, we should turn off eMMC　if storage is NVMe SSD.

BUG=b:170592992
BRANCH=zork
TEST=1. emerge-zork coreboot
     2. Check eMMC is enabled or disabled based on the eMMC bit in
        FW_CONFIG.

Change-Id: I7aeabc98fc16bc2837c8dcdc40c3c6a80898cdc9
Signed-off-by: Kevin Chiu <kevin.chiu@quantatw.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46292
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Rob Barnes <robbarnes@google.com>

src/mainboard/google/zork/variants/berknip/Makefile.inc

@@ -3,3 +3,4 @@
 subdirs-y += ./spd
 
 ramstage-y += gpio.c
+ramstage-y += variant.c

src/mainboard/google/zork/variants/berknip/variant.c

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <baseboard/variants.h>
+
+void variant_devtree_update(void)
+{
+	struct soc_amd_picasso_config *cfg;
+
+	cfg = config_of_soc();
+
+	/*
+	 * Enable eMMC if eMMC bit is set in FW_CONFIG or device is unprovisioned.
+	 */
+	if (!(variant_has_emmc() || boot_is_factory_unprovisioned()))
+		cfg->emmc_config.timing = SD_EMMC_DISABLE;
+}