MdeModulePkg/PartitionDxe: Merge the discovery of ElTorito into UDF

MdeModulePkg/PartitionDxe: Merge the discovery of ElTorito into UDF

In order to create all of the children (El Torito standard and UDF) for
a CD/DVD media in an entry of the PartitionDriverBindingStart(), this
commit merges the discovery of the El Torito feature
(PartitionInstallElToritoChildHandles) into function
PartitionInstallUdfChildHandles.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Paulo Alcantara <pcacjr@zytor.com>