kernel: Add support for custom dtbimage generation rules

#

#   BOARD_DTBO_CFG                     = Path to a mkdtboimg.py config file

#

#   BOARD_CUSTOM_DTBIMG_MK             = Path to a custom dtbimage makefile

#

#   BOARD_CUSTOM_DTBOIMG_MK            = Path to a custom dtboimage makefile

#

#   KERNEL_CC                          = The C Compiler used. This is automatically set based

endif # TARGET_NEEDS_DTBOIMAGE/BOARD_KERNEL_SEPARATED_DTBO

ifeq ($(BOARD_INCLUDE_DTB_IN_BOOTIMG),true)

ifneq ($(BOARD_CUSTOM_DTBIMG_MK),)

include $(BOARD_CUSTOM_DTBIMG_MK)

else

ifeq ($(BOARD_PREBUILT_DTBIMAGE_DIR),)

$(DTB_OUT):

	mkdir -p $(DTB_OUT)

endif # !TARGET_WANTS_EMPTY_DTB

endif # !BOARD_PREBUILT_DTBIMAGE_DIR

endif # BOARD_CUSTOM_DTBIMG_MK

endif # BOARD_INCLUDE_DTB_IN_BOOTIMG

endif # FULL_KERNEL_BUILD