MdeModulePkg/PartitionDxe: Put the UDF check ahead of MBR

MdeModulePkg/PartitionDxe: Put the UDF check ahead of MBR

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2823

Refer to UEFI spec 2.8, Section 13.3.2, a block device should
be scanned as below order:
1. GPT
2. ISO 9660 (El Torito) (UDF should aslo be here)
3. MBR
4. no partition found
Note: UDF is using the same boot method as CD, so put it in
the same priority with ISO 9660.

This would also solve the issue that ISO image with MBR would
be treat as MBR device instead of CD/DVD. That would make the
behavior of the image boot different:
If the CD/DVD's MBR be handled correctly, it would be enumerated
as a bootable device with MBR path and FAT filesystem. Some Linux
Distributions boot from such path (FAT with MBR path for ISO) would
come into the grub console instead of the installation selection.
With this change, the CD/DVD would always be enumerated with CD path.
And it would always boot to the installation selection.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Gary Lin <glin@suse.com>
Cc: Andrew Fish <afish@apple.com>
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>
Tested-by: Gary Lin <glin@suse.com>