MIPS: ZBOOT: Support LZ4 compression scheme

Add support for the LZ4 compression scheme in the ZBOOT decompression
stub, in order to support it we need to:

- select the "lz4" compression tool to compress the vmlinux.bin
  payload
- memcpy() is also required for decompress_unlz4.c so we share the
  implementation between GZIP, XZ and now LZ4

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: blogic@openwrt.org
Cc: james.hogan@imgtec.com
Patchwork: https://patchwork.linux-mips.org/patch/5829/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -1489,6 +1489,7 @@ config SYS_SUPPORTS_ZBOOT
 	bool
 	select HAVE_KERNEL_GZIP
 	select HAVE_KERNEL_BZIP2
+	select HAVE_KERNEL_LZ4
 	select HAVE_KERNEL_LZMA
 	select HAVE_KERNEL_LZO
 	select HAVE_KERNEL_XZ

arch/mips/boot/compressed/Makefile

@@ -48,6 +48,7 @@ $(obj)/vmlinux.bin: $(KBUILD_IMAGE) FORCE
 
 tool_$(CONFIG_KERNEL_GZIP)    = gzip
 tool_$(CONFIG_KERNEL_BZIP2)   = bzip2
+tool_$(CONFIG_KERNEL_LZ4)     = lz4
 tool_$(CONFIG_KERNEL_LZMA)    = lzma
 tool_$(CONFIG_KERNEL_LZO)     = lzo
 tool_$(CONFIG_KERNEL_XZ)      = xzkern

arch/mips/boot/compressed/decompress.c

@@ -43,7 +43,8 @@ void error(char *x)
 /* activate the code for pre-boot environment */
 #define STATIC static
 
-#if defined(CONFIG_KERNEL_GZIP) || defined(CONFIG_KERNEL_XZ)
+#if defined(CONFIG_KERNEL_GZIP) || defined(CONFIG_KERNEL_XZ) || \
+	defined(CONFIG_KERNEL_LZ4)
 void *memcpy(void *dest, const void *src, size_t n)
 {
 	int i;
@@ -72,6 +73,10 @@ void *memset(void *s, int c, size_t n)
 #include "../../../../lib/decompress_bunzip2.c"
 #endif
 
+#ifdef CONFIG_KERNEL_LZ4
+#include "../../../../lib/decompress_unlz4.c"
+#endif
+
 #ifdef CONFIG_KERNEL_LZMA
 #include "../../../../lib/decompress_unlzma.c"
 #endif