OvmfPkg: PlatformDxe: set preferred video resolution from platform config

The GraphicsConsoleDxe driver (in MdeModulePkg/Universal/Console)
determines the preferred video resolution from the dynamic PCDs
- gEfiMdeModulePkgTokenSpaceGuid.PcdVideoHorizontalResolution
- gEfiMdeModulePkgTokenSpaceGuid.PcdVideoVerticalResolution

Setting the graphics resolution during boot is useful when the guest OS
(for lack of a dedicated display driver) continues to work with the
original GOP resolution and framebuffer.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15366 6f19259b-4bc3-4df7-8a09-765794883524