mb/x/acpi_tables: Move EC_RW detection

These boards without ChromeEC do not set ACTIVE_EC_RW
flag as part of the gnvs_assign_chromeos() function.
Create abstraction to avoid <vendorcode/chromeos/x> include.

Change-Id: Ic6029e1807fcfe7dd2c766ce8221e347b6b096f9
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48777
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/acpi/chromeos-gnvs.c

@@ -18,3 +18,12 @@ void gnvs_assign_chromeos(void)
 	if (CONFIG(EC_GOOGLE_CHROMEEC) && !google_ec_running_ro())
 		gnvs_chromeos->vbt2 = ACTIVE_ECFW_RW;
 }
+
+void gnvs_set_ecfw_rw(void)
+{
+	chromeos_acpi_t *gnvs_chromeos = gnvs_chromeos_ptr(acpi_get_gnvs());
+	if (!gnvs_chromeos)
+		return;
+
+	gnvs_chromeos->vbt2 = ACTIVE_ECFW_RW;
+}