Put libmount library in subpackage libmount, mount utilities in
subpackage mount-utils, libfdisk in subpackage libfdisk, and fdisk
utilities in subpackage fdisk.
On my aarch64 device, /system/bin/mount is unable to handle logical
volumes (tries to access the non-existing /etc/fstab and errors), so
lets add our own libmount package.
Enabling libmount also enables the lsblk utility, which we put in
blk-utils.
