miniroot.kmod install fs + amd64cd.iso changes

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

Hi lists,

Here's a patch to bring amd64 closer (perhaps even "on par") with i386 
regarding INSTALL kernels, ISOs, and miniroot.kmod.

Basically, I reused most of what I found in i386 and sparc64 for 
image/kmod builds, and adapted to amd64. Given the portability of the 
copy/pasted code though, it was fairly trivial. I took also the 
boot.cfg.in default layouts from i386.

I tested the amd64cd.iso and miniroot.kmod installation module within a 
QEMU, they both worked fine.

I left the INSTALL config(5), but removed it from default release 
build.

Such a change will be announced with a HEADS-UP, and I'll update 
documentation consequently -- now that INSTALL is not built anymore, 
people should be informed about miniroot.kmod swtich.

Any comment before commit?

--
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost