General format for the 'umount' command:
    vitis umount -i <filesystem_image>
    vitis umount -b <block_device>
    vitis umount -m <mount_point>
    vitis umount --force

This command unmounts a Vitis filesystem image.
The command can be used in three ways:
    the '-i' option specifies the path to the file serving as the FS image;
    the '-b' option specifies the block device with ext4;
    the '-m' option specifies the mount point;
    with the '--force' parameter, all mount points are unmounted.
