OvmfPkg: non-null PcdLib instance for GraphicsConsoleDxe

OvmfPkg: non-null PcdLib instance for GraphicsConsoleDxe

GraphicsConsoleDxe (a UEFI_DRIVER under MdeModulePkg/Universal/Console)
determines the preferred video resolution from the dynamic PCDs
- gEfiMdeModulePkgTokenSpaceGuid.PcdVideoHorizontalResolution
- gEfiMdeModulePkgTokenSpaceGuid.PcdVideoVerticalResolution

In one of the next patches, we'd like to change these PCDs. In order for
GraphicsConsoleDxe to retrieve the new values dynamically,
- it must be linked with the non-null instance of PcdLib,
- OvmfPkg must provide dynamic defaults.

We keep MdeModulePkg's 800x600 default resolution. (The UEFI specification
requires video drivers to support 800x600.)

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@15362 6f19259b-4bc3-4df7-8a09-765794883524