ec/google/chromeec: Add .scan_bus() callback for Chrome EC device

This change adds scan_static_bus() as .scan_bus() callback for Chrome EC
device which allows scanning of devices sitting behind the EC using
the topology provided by mainboard's devicetree.cb.

BUG=b:154290952
TEST=Verified with follow-up changes that devices behind EC are scanned
correctly.

Signed-off-by: Furquan Shaikh <furquan@google.com>
Change-Id: Id3630db56774fba1e3fc53bf349588c4c585773b
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40514
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/ec/google/chromeec/ec_lpc.c

@@ -439,6 +439,7 @@ static struct device_operations ops = {
 	.init             = lpc_ec_init,
 	.read_resources   = lpc_ec_read_resources,
 	.set_resources    = noop_set_resources,
+	.scan_bus         = scan_static_bus,
 #if CONFIG(HAVE_ACPI_TABLES)
 	.acpi_name        = google_chromeec_acpi_name,
 	.acpi_fill_ssdt   = google_chromeec_fill_ssdt_generator,