mb/google/corsola: implement get_ec_is_trusted

Set VB2_CONTEXT_EC_TRUSTED in verstage_main.

TEST=build pass
BUG=b:202871018

Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Change-Id: If2837f5db52f91f5418d222d4dcd1af2aebcc105
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59942
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

src/mainboard/google/corsola/chromeos.c

@@ -26,3 +26,9 @@ void fill_lb_gpios(struct lb_gpios *gpios)
 	};
 	lb_add_gpios(gpios, chromeos_gpios, ARRAY_SIZE(chromeos_gpios));
 }
+
+int get_ec_is_trusted(void)
+{
+	/* EC is trusted if not in RW. This is active low. */
+	return !!gpio_get(GPIO_EC_IN_RW);
+}