feat(qemu): add efi_secret driver

Despite the generic name, the only current use of the `efi_secret`
is exposing data in /sys that's been injected into a SEV/SEV-ES
virtual machine. More info:

https://docs.kernel.org/security/secrets/coco.html

This secret is probably a luks password, so we need this driver at
boot time.

Signed-off-by: Cole Robinson <crobinso@redhat.com>

modules.d/90qemu/module-setup.sh

@@ -18,5 +18,6 @@ installkernel() {
         virtio_blk virtio virtio_ring virtio_pci \
         virtio_scsi virtio_console virtio_rng virtio_mem \
         spapr-vscsi \
-        qemu_fw_cfg
+        qemu_fw_cfg \
+        efi_secret
 }