OvmfPkg: VIRTIO_DEVICE_PROTOCOL: widen the Features bitmap to 64 bits

OvmfPkg: VIRTIO_DEVICE_PROTOCOL: widen the Features bitmap to 64 bits

The virtio-1.0 spec widens the Features bitmap to 64 bits. Modify the
declarations of the GetDeviceFeatures() and SetGuestFeatures() protocol
member functions accordingly.

Normally, a protocol cannot be changed in incompatible ways if the GUID
stays the same; however, we've always been extremely clear that
VIRTIO_DEVICE_PROTOCOL is internal to edk2. See for example the top of
"OvmfPkg/Include/Protocol/VirtioDevice.h".

In this patch, all producers and consumers of the GetDeviceFeatures() and
SetGuestFeatures() protocol members are updated.

The drivers that currently produce these members are "legacy" drivers (in
virtio-1.0 terminology), and they cannot (and will not) handle feature
bits above BIT31. Therefore their conversion is only for compatibility
with the modified protocol interface. The consumers will be responsible
for checking the VIRTIO_DEVICE_PROTOCOL.Revision field, and for not
passing feature bits that these backends cannot handle.

The VirtioMmioGetDeviceFeatures() implementation stores the result of an
MmioRead32() call with normal assignment, so it needs no change beyond
adapting its prototype.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>