systemd: depend on util-linux-mkswap

systemd: depend on util-linux-mkswap

busybox mkswap doesn't support all needed options.
Fixes:

systemd[1]: Activating swap /dev/disk/by-uuid/38d0b388-9989-4744-8a0a-3e6be1135f5a...
swapon[210]: swapon: /dev/sda3: swap format pagesize does not match.
swapon[210]: swapon: /dev/sda3: reinitializing the swap.
swapon[212]: mkswap: invalid option -- 'U'
swapon[212]: BusyBox v1.37.0 () multi-call binary.
swapon[212]: Usage: mkswap [-L LBL] BLOCKDEV [KBYTES]
systemd[1]: dev-disk-by\x2duuid-38d0b388\x2d9989\x2d4744\x2d8a0a\x2d3e6be1135f5a.swap: Swap process exited, code=exited,

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>