OvmfPkg/VirtioRngDxe: negotiate VIRTIO_F_IOMMU_PLATFORM

OvmfPkg/VirtioRngDxe: negotiate VIRTIO_F_IOMMU_PLATFORM

VirtioRngDxe driver has been updated to use IOMMU-like member functions
from VIRTIO_DEVICE_PROTOCOL to translate the system physical address to
device address. We do not need to do anything special when
VIRTIO_F_IOMMU_PLATFORM bit is present hence treat it in parallel with
VIRTIO_F_VERSION_1.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>