kernel: Move TARGET_KERNEL_ADDITIONAL_FLAGS to kernel task

* Currently, because DTC_EXT make flag is in the
   kernel task the only way to override it is to
   have TARGET_KERNEL_ADDITIONAL_FLAGS come after.

Change-Id: If62ed979581dc07eafd4628ce2b2d799388d3704

build/tasks/kernel.mk

@@ -21,6 +21,7 @@
 #
 # These config vars are usually set in BoardConfig.mk:
 #
+#   TARGET_KERNEL_ADDITIONAL_FLAGS     = Additional make flags, optional
 #   TARGET_KERNEL_CONFIG               = List of kernel defconfigs, first one being the base one,
 #                                          while all the others are fragments that will be merged
 #                                          to main one in .config.
@@ -255,6 +256,10 @@ ifeq (true,$(filter true, $(TARGET_NEEDS_DTBOIMAGE) $(BOARD_KERNEL_SEPARATED_DTB
     KERNEL_MAKE_FLAGS += DTC_EXT=$(KERNEL_BUILD_OUT_PREFIX)$(DTC)
 endif
 
+ifneq ($(TARGET_KERNEL_ADDITIONAL_FLAGS),)
+    KERNEL_MAKE_FLAGS += $(TARGET_KERNEL_ADDITIONAL_FLAGS)
+endif
+
 # Internal implementation of make-kernel-target
 # $(1): output path (The value passed to O=)
 # $(2): target to build (eg. defconfig, modules, dtbo.img)

config/BoardConfigKernel.mk

@@ -135,10 +135,6 @@ else
   KERNEL_MAKE_FLAGS += CPATH="/usr/include:/usr/include/x86_64-linux-gnu" HOSTCFLAGS="-fuse-ld=lld" HOSTLDFLAGS="-L/usr/lib/x86_64-linux-gnu -L/usr/lib64 -fuse-ld=lld"
 endif
 
-ifneq ($(TARGET_KERNEL_ADDITIONAL_FLAGS),)
-  KERNEL_MAKE_FLAGS += $(TARGET_KERNEL_ADDITIONAL_FLAGS)
-endif
-
 TOOLS_PATH_OVERRIDE := \
     LD_LIBRARY_PATH=$(BUILD_TOP)/prebuilts/tools-lineage/$(HOST_PREBUILT_TAG)/lib:$$LD_LIBRARY_PATH \
     PERL5LIB=$(BUILD_TOP)/prebuilts/tools-lineage/common/perl-base