libpayload: Add LZ4 decompression algorithm

This patch adds support for the LZ4 decompression algorithm to
libpayload. It's what all the cool kids are using for decompression
these days and has many interesting advantages over LZMA (and everything
else I know of): blazing fast decompression (20(!) times faster than
LZMA, twice as fast as LZO on my Cortex-A72), no memory requirements on
decompression, and possibly in-place decompression support. It pays for
that with a lower compression ratio (about 50% larger compressed size
than LZMA, 10% larger than LZO for an ARM64 Linux kernel binary), but
the boot time math still works in its favor for our IO speeds.

This patch only adds the raw decompression functions for use by external
payloads, we can later try integrating them in CBFS. It copies the
decompression code itself unmodified from the upstream LZ4 library at
github.com/Cyan4973/lz4 which will hopefully make it easy to update. The
frame format parsing is reimplemented since the upstream version looks
unnecessarily complex and unreadable for our needs.

BRANCH=smaug
BUG=chrome-os-partner:32184
TEST=With other patches, booted ARM64 kernel that got compressed from
15M to 5.1M and decompresses in 44ms.

Change-Id: I65bdc4b2b19bd51c7b7e17a4e4b79da301a2a014
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: f8a1fc996d5b0234d07f567fa8163d0f802d5144
Original-Change-Id: I15c0620da05561ade2552b15ffdf6bb3afd7eb26
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/282743
Original-Reviewed-by: Stefan Reinauer <reinauer@google.com>
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10845
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

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