Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/csky/boot/Makefile b/arch/csky/boot/Makefile
new file mode 100644
index 0000000..dbc9b1b
--- /dev/null
+++ b/arch/csky/boot/Makefile
@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: GPL-2.0-only
+targets := Image zImage uImage
+targets += $(dtb-y)
+
+$(obj)/Image: vmlinux FORCE
+	$(call if_changed,objcopy)
+	@echo '  Kernel: $@ is ready'
+
+compress-$(CONFIG_KERNEL_GZIP) = gzip
+compress-$(CONFIG_KERNEL_LZO)  = lzo
+compress-$(CONFIG_KERNEL_LZMA) = lzma
+compress-$(CONFIG_KERNEL_XZ)   = xzkern
+compress-$(CONFIG_KERNEL_LZ4)  = lz4
+
+$(obj)/zImage:  $(obj)/Image FORCE
+	$(call if_changed,$(compress-y))
+	@echo '  Kernel: $@ is ready'
+
+UIMAGE_ARCH		= sandbox
+UIMAGE_COMPRESSION	= $(compress-y)
+UIMAGE_LOADADDR		= $(shell $(NM) vmlinux | awk '$$NF == "_start" {print $$1}')
+
+$(obj)/uImage: $(obj)/zImage
+	$(call if_changed,uimage)
+	@echo 'Image: $@ is ready'