Platform/Sgi: Add _OSC method for RD-V1

Add ACPI Operating System Capabilities (_OSC) control method for
reporting platform-wide capabilities on RD-V1 platform both in single
chip and in multi chip mode.

Signed-off-by: Pranav Madhu <Pranav.Madhu@arm.com>
Change-Id: I62d6d00234c44cc5e717a5071200e9bec4649740