fix(mediatek): wrap cold_boot.h with MTK_SIP_KERNEL_BOOT_ENABLE

We should wrap cold_boot.h with MTK_SIP_KERNEL_BOOT_ENABLE to avoid
build error.

Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Change-Id: Idfd760fbb7c782d4fc9de674d86a7123e0129c0d
diff --git a/plat/mediatek/common/mtk_smc_handlers.c b/plat/mediatek/common/mtk_smc_handlers.c
index 24b978c..51a960f 100644
--- a/plat/mediatek/common/mtk_smc_handlers.c
+++ b/plat/mediatek/common/mtk_smc_handlers.c
@@ -6,9 +6,11 @@
 
 #include <assert.h>
 #include <errno.h>
+#if MTK_SIP_KERNEL_BOOT_ENABLE
+#include <cold_boot.h>
+#endif
 #include <common/debug.h>
 #include <common/runtime_svc.h>
-#include <cold_boot.h>
 #include <lib/mtk_init/mtk_init.h>
 #include <mtk_sip_svc.h>