Update of wip/sddm to version 0.21

[Stepan Ipatov <st.ipatov%gmail.com@localhost>]

Hi,

I have updated wip/sddm to version 0.21. I have been using it daily on 
my laptop for a couple of months now, and it seems to work reasonably 
well on NetBSD.

Could one of the experienced maintainers please take a look and check 
whether it is ready to be moved into the main pkgsrc repository?

--
Thanks in advance,
  Stepan Ipatov