Make hardlinking kernel-devel optional

[Ralf Ertzinger <fedora camperquake de>]

Hi.

I't like to request to make the hardlink stage kernel-devel does on every
install optional. It takes a damn lot of time on my not-too-fast machines,
I do not exactly care about the saved disk space, and given the rate of
kernel changes in rawhide there are a lot of wasted CPU cycles there.

There is a /etc/sysconfig/kernel, how about dropping a "HARDLINK=yes/no"
there?