Add LZO decompressor support

This patch adds LZO decompression support to U-Boot. It is needed for
the upcoming UBIFS support, since UBIFS uses LZO as default compressor/
decompressor. Since we only support read-only in UBIFS, only the
decompressor is needed.

All this is copied with minor changes from the current Linux kernel
version (2.6.28-rc8).

This patch only implements this LZO decompressor support for PPC.
Other platforms using UBIFS will have to add the required
"include/asm/unaligned.h" as well. It should be fairly easy to copy this
from the Linux source tree as I have done it for PPC in this patch.

Signed-off-by: Stefan Roese <sr@denx.de>