bcache: Prune struct btree_op

Eventual goal is for struct btree_op to contain only what is necessary
for traversing the btree.

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

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

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

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

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

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

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

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

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

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

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

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