bcache: Add on error panic/unregister setting

Works kind of like the ext4 setting, to panic or remount read only on
errors.

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

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

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

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

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