mb/google/rex: Add Write Protect GPIO to cros_gpios

This will enable crossystem to access WP GPIO

BUG=b:258048687
TEST= wpsw_cur in crossystem reads the correct gpio

Change-Id: I67f4a57025064dbf8c691255b0abae9d3fa0dbd3
Signed-off-by: Ivy Jian <ivy.jian@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69468
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/rex/variants/rex0/gpio.c

@@ -492,6 +492,8 @@ const struct pad_config *variant_romstage_gpio_table(size_t *num)
 	}
 }
 
-static const struct cros_gpio cros_gpios[] = {};
+static const struct cros_gpio cros_gpios[] = {
+	CROS_GPIO_WP_AH(GPIO_PCH_WP, CROS_GPIO_DEVICE_NAME),
+};
 
 DECLARE_WEAK_CROS_GPIOS(cros_gpios);