Add lz4hc image compression format

Smaller than lz4 and decompresses at the same speed. Compression is
a bit slower.

Example saves on old FB APK:
Uncompressed: 44748800 bytes
LZ4: 12443648 bytes
LZ4HC: 11055104 bytes

Generating the image slows down by ~1s per 20MB of image due to
slower compression. Decompression is about the same speed but there
should be a slight speedup since less data needs to be read from
flash.

Added test.

Bug: 22858531

Change-Id: Ib2704305b9bec5b0ba3b1e871f59f4eedff330b7