OvmfPkg/VirtioGpuDxe: map virtio GPU command objects to device addresses

OvmfPkg/VirtioGpuDxe: map virtio GPU command objects to device addresses

Every virtio GPU command used by VirtioGpuDxe is synchronous and formatted
as a two-descriptor chain: request, response. The internal workhorse
function that all the command-specific functions call for such messaging
is VirtioGpuSendCommand().

In VirtioGpuSendCommand(), map the request from system memory to bus
master device address for BusMasterRead operation, and map the response
from system memory to bus master device address for BusMasterWrite
operation.

Pass the bus master device addresses to VirtioAppendDesc(). (See also
commit 4b725858de68, "OvmfPkg/VirtioLib: change the parameter of
VirtioAppendDesc() to UINT64", 2017-08-23.)

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