soc/mediatek/mt8196: Initialize mt6685 PMIF for RTC read/write API

RTC read/write API requires mt6685 PMIF initialization to prevent
assertion from rtc_get().

BUG=b:382351678
TEST=Build pass, boot successfully, boot log show:
[INFO ]  [mt6685_init_pmif_arb]CHIP ID = 0x85

Change-Id: I4b0298e71c2c270e0c48723755319348928ac1af
Signed-off-by: Jarried Lin <jarried.lin@mediatek.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86155
Reviewed-by: Yidi Lin <yidilin@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

src/soc/mediatek/mt8196/soc.c

@@ -8,6 +8,7 @@
 #include <soc/gpueb.h>
 #include <soc/mcupm.h>
 #include <soc/mmu_operations.h>
+#include <soc/mt6685.h>
 #include <soc/mtk_fsp.h>
 #include <soc/pcie.h>
 #include <soc/sspm.h>
@@ -44,6 +45,7 @@ static void soc_init(struct device *dev)
 	sspm_init();
 	gpueb_init();
 	mcupm_init();
+	mt6685_init_pmif_arb();
 }
 
 static struct device_operations soc_ops = {