btrfs: switch BTRFS_ROOT_* to enums

We can use simple enum for values that are not part of on-disk format:
root tree flags.

Reviewed-by: Omar Sandoval <[email protected]>
Reviewed-by: Qu Wenruo <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>
Signed-off-by: David Sterba <[email protected]>
1 file changed