ArmPlatformPkg/ArmFvpDxe: Added Virtio Block support

ArmPlatformPkg/ArmFvpDxe: Added Virtio Block support

Right now the ARM Platform driver does not do much, but
I expect to move most platform specific code into platform
specific driver in the future.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
v5:
- ensure / document that the VIRTIO_BLK_DEVICE_PATH structure must be
  packed
- fix whitespace damage in definition of "mVirtioBlockDevicePath"
- the platform driver is added to all platform DSC and FDF files in the
  previous patch; this patch focuses on virtio only

Change-Id: I3505bfc5b31085b8017bd9e6895a155bd7a2eee9
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-By: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14981 6f19259b-4bc3-4df7-8a09-765794883524