Platform/Sgi: Fix ACPI Low Power Idle states for RD-V1

Fix the ACPI _LPI object's control method for RD-V1 platform. This
platform supports only the platform co-ordinated LPI. Accordingly,
correct the LPI Level ID value. Additionally, as this platform does not
support residency counter, clear the residency counter frequency from
_LPI object's control method. Clear the enable parent state field as
well as there is no parent state available.

Change-Id: Ic13d7267fb54b336058a48ababca7ae69ce9accd
Signed-off-by: Pranav Madhu <pranav.madhu@arm.com>