arm: add support for LZ4-compressed kernel

Integrates the LZ4 decompression code to the arm pre-boot code.

Signed-off-by: Kyungsik Lee <kyungsik.lee@lge.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Florian Fainelli <florian@openwrt.org>
Cc: Yann Collet <yann.collet.73@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/x86/boot.txt

@@ -657,9 +657,10 @@ Protocol:	2.08+
   uncompressed data should be determined using the standard magic
   numbers.  The currently supported compression formats are gzip
   (magic numbers 1F 8B or 1F 9E), bzip2 (magic number 42 5A), LZMA
-  (magic number 5D 00), and XZ (magic number FD 37).  The uncompressed
-  payload is currently always ELF (magic number 7F 45 4C 46).
-  
+  (magic number 5D 00), XZ (magic number FD 37), and LZ4 (magic number
+  02 21).  The uncompressed payload is currently always ELF (magic
+  number 7F 45 4C 46).
+
 Field name:	payload_length
 Type:		read
 Offset/size:	0x24c/4