decompressor: Add LZ4 decompressor module
This patch adds support for LZ4 decompression in the Linux Kernel.
LZ4 Decompression APIs for kernel are based on LZ4 implementation
by Yann Collet.

LZ4 homepage : http://fastcompression.blogspot.com/p/lz4.html
LZ4 source repository : http://code.google.com/p/lz4/

Signed-off-by: Kyungsik Lee <kyungsik.lee@lge.com>

v2:
- Clean up code
- Enable unaligned access for ARM v6 and above with
  CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
- Add lz4_decompress() for faster decompression with
  uncompressed output size
v3:
- Fix indent errors
- Prevent double evaluation by using an inline function