bcachefs: Rename KEY_TYPE_whiteout -> KEY_TYPE_hash_whiteout

Snapshots are going to need a different whiteout key type. Also, switch
to using BCH_BKEY_TYPES() to define the bkey value accessors.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
6 files changed