MdeModulePkg/PciBus: Refine EFI_PCI_ROM_IMAGE_MAPPING

The patch doesn't impact real functionality.
It only renames EFI_PCI_ROM_IMAGE_MAPPING to PCI_ROM_IMAGE,
and changes prototype of PciRomAddImageMapping so that
no explicit type cast is needed when calling this function.

It also removes unused field RomBase from PCI_IO_DEVICE structure.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.h

@@ -1,7 +1,7 @@
 /** @file
   Header files and data structures needed by PCI Bus module.
 
-Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
 This program and the accompanying materials
 are licensed and made available under the terms and conditions of the BSD License
 which accompanies this distribution.  The full text of the license may be found at
@@ -239,11 +239,6 @@ struct _PCI_IO_DEVICE {
   //
   UINT64                                    RomSize;
 
-  //
-  // The OptionRom Size
-  //
-  UINT64                                    RomBase;
-
   //
   // TRUE if all OpROM (in device or in platform specific position) have been processed
   //