OvmfPkg: clone PciHostBridgeDxe from PcAtChipsetPkg

OvmfPkg: clone PciHostBridgeDxe from PcAtChipsetPkg

The source code is copied verbatim, with the following two exceptions:
- the UNI files are dropped, together with the corresponding UNI
  references in the INF file,
- the INF file receives a new FILE_GUID.

The OVMF DSC and FDF files are at once flipped to the cloned driver.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17951 6f19259b-4bc3-4df7-8a09-765794883524