redhat/configs: Support the virtio_mmio.device parameter in Fedora

This setting enables support for the device parameter of the module virtio_mmio, which isn't loaded on most systems. This parameter is automatically added to systems booted with the Firecracker VMM to locate its VirtIO devices, so this change allows the Fedora kernel to use the virtual hardware when booted as a guest. It is left disabled for RHEL since the virtio_mmio module is not built there.

There is some context for this on the Fedora developer list. This is an optional but nice to have feature for using Firecracker on Fedora.