MdeModulePkg/PciBus: Remove unnecessary PCIE detection

MdeModulePkg/PciBus: Remove unnecessary PCIE detection

CreatePciIoDevice() detects whether the PCI device is a PCI Express
device and remembers the device type in PciIoDevice->IsPciExp.

RegisterPciDevice() detects the device type again which is
unnecessary. The detection logic can be removed.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>