btrfs: prepare incompat flags for more compression methods

Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs: lz4: add wrapper functions and enable it

Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs: add lz4hc incompat bits

Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs: add lz4hc wrapper and enable it

Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs: reduce duplicate code in lz4_wrapper.c

Add generic functions for compress_pages and alloc that accept an argument to
enable high compression, and replace the lz4/lz4hc variants of both with
wrappers for these.

Signed-off-by: Andrew Mahone <andrew.mahone@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.cz>