mb/google/rauru: Disable modem power

BUG=b:315894234
TEST=Build pass.
The actual measurement of the average power over 20 seconds decreased
from 6.755W to 6.716W.

Change-Id: I71bda7055afc902525501ddf7074f9b2c5550d4a
Signed-off-by: Xavier Chang <xavier.chang@mediatek.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/85663
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Yidi Lin <yidilin@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/rauru/romstage.c

@@ -3,6 +3,7 @@
 #include <arch/stages.h>
 #include <soc/emi.h>
 #include <soc/irq2axi.h>
+#include <soc/modem_power_ctrl.h>
 #include <soc/mt6316.h>
 #include <soc/mt6363.h>
 #include <soc/mt6373.h>
@@ -33,6 +34,7 @@ void platform_romstage_main(void)
 	mt6373_init();
 	mt6685_init();
 	mtk_dram_init();
+	modem_power_down();
 
 	if (CONFIG(PCI))
 		mtk_pcie_deassert_perst();