* extras/packaging/gnu-linux/Makefile (GUIX_PACK_FORMATS): New
variable.
(guix-pack-command): Add format argument.  Make the --postinst-file
argument conditional to the 'deb' format.
(define-deb-pack-rule): Rename to...
(define-guix-pack-rule): ... this.  Add a new format argument, and
move existing architecture argument into 2nd position.
* extras/packaging/gnu-linux/scripts/deploy-packages.sh
(package): Register 'guix-rpm-pack' as RPM packages.

Change-Id: I1b5501c02e917b2b0c5e92e775a85478dd67316e