superio/ite/it8728f: RAMstage PNP configuration component

Provide devicetree.cb RAMstage configuration of this superio component.

Change-Id: I376d2fb6dafc301cbc437518012f8c43b0af4be2
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/5668
Tested-by: build bot (Jenkins)
Reviewed-by: Rudolf Marek <r.marek@assembler.cz>