Btrfs: make compress and nodatacow mount options mutually exclusive

If a filesystem is mounted with compression and then remounted by adding nodatacow,
the compression is disabled but the compress flag is still visible.
Also, if a filesystem is mounted with nodatacow and then remounted with compression,
nodatacow flag is still present but it's not active.
This patch:
- removes compress flags and notifies that the compression has been disabled if the
  filesystem is mounted with nodatacow
- removes nodatacow and nodatasum flags if mounted with compress.

Signed-off-by: Andrei Popa <andrei.popa@i-neo.ro>