mediatek: Separate WDT reset function from WDT driver

Separate WDT reset function from WDT driver, then we can use the common
WDT driver and have a board-specific reset function on different boards.

In Kukui, we plan to use GPIO HW reset, instead of WDT reset. Add config
"MISSING_BOARD_RESET" in Kukui to pass the build for now.

BUG=b:80501386
BRANCH=none
TEST=emerge-elm coreboot; emerge-kukui coreboot;

Change-Id: Ica07fe3a027cd7e9eb6d10202c3ef3ed7bea00c2
Signed-off-by: Tristan Shieh <tristan.shieh@mediatek.com>
Reviewed-on: https://review.coreboot.org/c/31121
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/mediatek/common/wdt.c

@@ -15,13 +15,9 @@
 
 #include <arch/io.h>
 #include <console/console.h>
-#include <reset.h>
-#include <soc/addressmap.h>
 #include <soc/wdt.h>
 #include <vendorcode/google/chromeos/chromeos.h>
 
-static struct mtk_wdt_regs *const mtk_wdt = (void *)RGU_BASE;
-
 int mtk_wdt_init(void)
 {
 	uint32_t wdt_sta;
@@ -56,8 +52,3 @@ int mtk_wdt_init(void)
 
 	return wdt_sta;
 }
-
-void do_board_reset(void)
-{
-	write32(&mtk_wdt->wdt_swrst, MTK_WDT_SWRST_KEY);
-}