[XOP-602] Add flag to make PDO non-removable

Default is for PDOs to be marked removable and surprise removable.
To mark a PDO as non-removable, add a DWORD value called Removable
with value 0 to
HKLM/System/CurrentControlSet/services/XENBUS/Parameters/<ClassName>

Signed-off-by: Owen Smith <owen.smith@citrix.com>