mb/google/rauru: Enable vcore DVFS in romstage

TEST=Build pass.
BUG=b:343878736

Change-Id: Idcd9754c1974f1d6fdb26d7c6af1e2863cb724f7
Signed-off-by: Kunlong Wang <kunlong.wang@mediatek.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86071
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yidi Lin <yidilin@google.com>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

src/mainboard/google/rauru/romstage.c

@@ -3,6 +3,7 @@
 #include <arch/stages.h>
 #include <soc/clkbuf_ctl.h>
 #include <soc/dvfs.h>
+#include <soc/dvfsrc.h>
 #include <soc/emi.h>
 #include <soc/irq2axi.h>
 #include <soc/modem_power_ctrl.h>
@@ -40,6 +41,7 @@ void platform_romstage_main(void)
 	mtk_fsp_init(ROMSTAGE_INIT);
 	mtk_fsp_load_and_run();
 	mt6685_init();
+	dvfsrc_opp_level_mapping();
 	srclken_rc_init();
 	clk_buf_init();
 	mtk_dram_init();