bcache: Add explicit keylist arg to btree_insert()

Some refactoring - better to explicitly pass stuff around instead of
having it all in the "big bag of state", struct btree_op. Going to prune
struct btree_op quite a bit over time.

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

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/request.c
Simple merge

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