mb/google/skywalker: Add thermal init flow in romstage

BUG=b:379008996
BRANCH=none
TEST=build pass, thermal init log:
[INFO ]  ===== lvts_thermal_init begin ======
[INFO ]  thermal_init: thermal initialized

Signed-off-by: Raymond Sun <raymond.sun@mediatek.corp-partner.google.com>
Change-Id: Id57f73206135f814f44b34290c5f2624ea56e1df
Reviewed-on: https://review.coreboot.org/c/coreboot/+/88442
Reviewed-by: Yidi Lin <yidilin@google.com>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/skywalker/romstage.c

@@ -10,6 +10,7 @@
 #include <soc/pmif.h>
 #include <soc/regulator.h>
 #include <soc/rtc.h>
+#include <soc/thermal.h>
 
 static void raise_little_cpu_freq(void)
 {
@@ -29,4 +30,5 @@ void platform_romstage_main(void)
 	rtc_boot();
 	dvfs_init();
 	mtk_dram_init();
+	thermal_init();
 }