ChromeOS: Add legacy mainboard_ec_running_ro()

Motivation is to have mainboard_chromeos_acpi_generate()
do nothing else than fill ACPI \OIPG package.

Change-Id: I3cb95268424dc27f8c1e26b3d34eff1a7b8eab7f
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58896
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/vendorcode/google/chromeos/chromeos.h

@@ -25,7 +25,6 @@ void mainboard_prepare_cr50_reset(void);
 void cbmem_add_vpd_calibration_data(void);
 void chromeos_set_me_hash(u32*, int);
 void chromeos_set_ramoops(void *ram_oops, size_t size);
-void chromeos_set_ecfw_rw(void);
 void chromeos_init_chromeos_acpi(void);
 
 /**