gfs2_jadd: Clean up definitions from linux/fs.h
    
    gfs2_mkfs.h defines some constants from linux/fs.h to avoid clashes with
    definitions pulled in my sys/mount.h. When gfs2_jadd started using
    FS_IOC_FIEMAP, it included linux/fs.h to get it which meant sparse
    started complaining about redefinitions again. To fix that, add the
    FS_IOC_FIEMAP definition to gfs2_mkfs.h and remove the linux/fs.h
    include. Also remove all the unused definitions from gfs2_mkfs.h to keep
    the workaround minimal.
    
    Signed-off-by: Andrew Price <anprice@redhat.com>