Btrfs: make btrfs acls selectable

This patch adds a menu entry to kconfig to enable acls for btrfs.
This allows you to enable FS_POSIX_ACL at kernel compile time.

(updated by Jeff Mahoney to make the changes in fs/btrfs/Kconfig instead)

Signed-off-by: Christian Hesse <mail@earthworm.de>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>