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