ShellPkg: Add DiskIO2, and fix GUID from string check to be case insensitive

- Add DiskIO2 to list of known protocols
- Fix string check to be case insensitive for commands like ‘dh –p protocolname’

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Chris Phillips <chrisp@hp.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14851 6f19259b-4bc3-4df7-8a09-765794883524