gnu: linux-initrd: Factorize device node creation.

* guix/build/linux-initrd.scm (make-essential-device-nodes): New
  procedure.
* gnu/packages/linux-initrd.scm (qemu-initrd): Use it.

gnu: linux-initrd: Make device nodes for QEMU's hard disk.

* gnu/packages/linux-initrd.scm (qemu-initrd): Make /dev/vda*.

gnu: linux-initrd: Make Guile modules accessible in the chroot.

* gnu/packages/linux-initrd.scm (qemu-initrd): Add (guix build utils) to
  #:modules, and use it.  Copy .scm and .go files to /root.
* guix/build/linux-initrd.scm (bind-mount): New procedure.

gnu: linux-initrd: Add (guix build linux-initrd) and use it.

* gnu/packages/linux-initrd.scm (qemu-initrd): Add #:modules argument.
  Factorize and move some of the code to...
* guix/build/linux-initrd.scm: ... here.  New file.
* Makefile.am (MODULES): Add it.

gnu: linux-initrd: Allow Guile modules to be embedded in the initrd.

* gnu/packages/linux-initrd.scm (raw-build-system): New macro.
  (module-package, compiled-module-package): New procedures.
  (expression->initrd): Add `modules' keyword parameter.
  Add "modules" and "modules/compiled" inputs; copy them onto the
  initrd.
* guix/derivations.scm (imported-modules, compiled-modules): Publicize.

gnu: Add support for Guile in Linux initrd.

* gnu/packages/linux-initrd.scm: New file.

gnu: Add support for Guile in Linux initrd.

* gnu/packages/linux-initrd.scm: New file.