powercap: intel_rapl: support new layout of Psys PowerLimit Register on SPR

On Sapphire Rapids, the layout of the Psys domain Power Limit Register
is different from from what it was before.

Enhance the code to support the new Psys PL register layout.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Reported-and-tested-by: Alkattan Dana <dana.alkattan@intel.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>