SDV: ZwRegistryOpen rule violations

SDV: ZwRegistryOpen rule violations

Dont hold the ParametersKey open, SDV treats this as a mismatched
ZwRegistryOpen and ZwClose pair.
Open the registry key when required, and close it once its no longer
required.

Signed-off-by: Owen Smith <owen.smith@citrix.com>
Remove DriverGetParametersKey() from xenfilt/driver.h and don't add the
implementation of DriverOpenParametersKey() in xenfilt/driver.c.

Signed-off-by: Paul Durrant <paul@xen.org>