Add support to decompress brotli compressed new data

Add a new writer that can decode the brotli-compressed system/vendor
new data stored in the OTA zip.

Brotli generally gives better compression rate at the cost of slightly
increased time consumption. The patch.dat is already compressed
by BZ; so there's no point to further compress it.

For the given 1.9G bullhead system image:
Size: 875M -> 787M; ~10% reduction of package size.
Time: 147s -> 153s; ~4% increase of the block_image_update execution time.
(I guess I/O takes much longer time than decompression.)

Also it takes 4 minutes to compress the system image on my local
machine, 3 more minutes than zip.

Test: recovery tests pass && apply a full OTA with brotli compressed
system/vendor.new.dat on bullhead

Change-Id: I232335ebf662a9c55579ca073ad45265700a621e