ShellPkg/hexeditor: Use CpuIo for memory access

ShellPkg/hexeditor: Use CpuIo for memory access

The original code uses PciRootBridgeIo for memory access.
It worked before MdeModulePkg/PciHostBridgeDxe driver was checked in.
But MdeModulePkg/PciHostBridgeDxe adds checks to ensure the MMIO
access request is in the scope of the current RootBridgeIo instance.
It causes "hexeditor -m 0 2" reports error because memory address 0
surely is not in the scope of any RootBridgeIo instance.
In fact only accessing the MMIO space occupied by the RootBridgeIo
can work.

The patch changes hexeditor to use CpuIo for memory access.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>