ovl: make path-type a bitmap

OVL_PATH_PURE_UPPER -> __OVL_PATH_UPPER | __OVL_PATH_PURE
OVL_PATH_UPPER      -> __OVL_PATH_UPPER
OVL_PATH_MERGE      -> __OVL_PATH_UPPER | __OVL_PATH_MERGE
OVL_PATH_LOWER      -> 0

Multiple R/O layers will allow __OVL_PATH_MERGE without __OVL_PATH_UPPER.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

diff --cc fs/overlayfs/copy_up.c
Simple merge

diff --cc fs/overlayfs/dir.c
Simple merge

diff --cc fs/overlayfs/inode.c
Simple merge

diff --cc fs/overlayfs/overlayfs.h
Simple merge

diff --cc fs/overlayfs/readdir.c
Simple merge

diff --cc fs/overlayfs/super.c
Simple merge