installer: Report known-unsupported PCI devices....* gnu/installer/hardware.scm: New file.
* gnu/local.mk (INSTALLER_MODULES): Add it.
* po/guix/POTFILES.in: Add it.
* gnu/installer.scm (installer-steps): Pass #:pci-database to the
'welcome' step procedure.
* gnu/installer/newt.scm (welcome-page): Add #:pci-database and pass it
to 'run-welcome-page'.
* gnu/installer/newt/welcome.scm (check-hardware-support): Add #:pci-database.
Enumerate unsupported PCI devices and run an error page when unsupported
devices are found.
(run-welcome-page): Add #:pci-database and pass it to
'check-hardware-support' and to the recursive call.
* gnu/installer/record.scm (<installer>)[welcome-page]: Adjust comment.
* doc/guix.texi (Hardware Considerations): Mention it.