soc/mediatek/mt8192: Add mt6315_romstage_init

Initialize pmif_arb in romstage.

BUG=b:177389446

Signed-off-by: Yidi Lin <yidi.lin@mediatek.com>
Change-Id: I3ffe7277c9ecb04269c832693d42799ba1711384
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49934
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

src/soc/mediatek/mt8192/include/soc/mt6315.h

@@ -35,6 +35,7 @@ enum {
 };
 
 void mt6315_init(void);
+void mt6315_romstage_init(void);
 void mt6315_buck_set_voltage(u32 slvid, u32 buck_id, u32 buck_uv);
 u32 mt6315_buck_get_voltage(u32 slvid, u32 buck_id);
 #endif /* __SOC_MEDIATEK_MT6315_H__ */

src/soc/mediatek/mt8192/mt6315.c

@@ -301,3 +301,8 @@ void mt6315_init(void)
 	mt6315_wdt_enable(MT6315_GPU);
 	mt6315_init_setting();
 }
+
+void mt6315_romstage_init(void)
+{
+	init_pmif_arb();
+}