bcache: Add struct bset_sort_state

More disentangling bset.c from the rest of the bcache code - soon, the
sorting routines won't have any dependencies on any outside structs.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

diff --cc drivers/md/bcache/bcache.h
Simple merge

diff --cc drivers/md/bcache/bset.c
Simple merge

diff --cc drivers/md/bcache/bset.h
Simple merge

diff --cc drivers/md/bcache/btree.c
Simple merge

diff --cc drivers/md/bcache/super.c
Simple merge

diff --cc drivers/md/bcache/sysfs.c
Simple merge