Fix 3 bugs in DiskIoDxe and PartitionDxe drivers introduced in DiskIo2 implementation.

Fix 3 bugs in DiskIoDxe and PartitionDxe drivers introduced in DiskIo2 implementation.
1. DiskIo2 shouldn't signal the event when the *Ex interface returns failure status per the UEFI spec.
2. PartitionDxe should close DiskIo2 protocol when error happens in DriverBindingStart() otherwise Fat driver cannot open the DiskIo2 BY_DRIVER.
3. PartitionDxe should create event using TPL_NOTIFY instead of TPL_CALLBACK otherwise asynchronous FileIo may be blocked.

Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14680 6f19259b-4bc3-4df7-8a09-765794883524