pkgbase: Move rc scripts and related files to their own packages

[manu]

Summary

It doesn't need to be in runtime and might help people who want to
experiment with other rc system or don't use one (like in small
embedded mfsroot).

[gjb]

I'm not sure I agree with this one. Moving required (in some sense of the word for certain things) from the main runtime package feels wrong to me.

[manu]

In D21499#468443, @gjb wrote:

I'm not sure I agree with this one. Moving required (in some sense of the word for certain things) from the main runtime package feels wrong to me.

I don't think that rc are required files. Again if I want to create a small mfsroot I just need to use the FreeBSD-runtime package and add my own /etc/rc.
A real world example is for example if you want to reroot on iSCSI, you will create the mfsroot based on the FreeBSD-runtime and FreeBSD-iscsi package and just add a /etc/rc that will reroot on it.

[gjb]

This one is another case of "I do not agree, but will not object."

[bapt]

We discussed with @manu about it and I do not agree as well, but do not object as he has an argument for people who work with replacing rc with something else. We can move that back to runtime later if needed.