vconsole-setup: do not require /etc/sysconfig/console

/etc/vconsole.conf is a perfectly valid way to configure
the consoles, we don't need /etc/sysconfig/console to be existing and
valid. It should be only read for compatibility if it exists.

Without this change systemd-vconsole-setup.service fails in
dracut-generated initramfs and on systems without /etc/sysconfig/console

Release: 9