nb/intel/haswell/gma: Use common init_igd_opregion method

Use common init_igd_opregion method and remove duplicated code in
acpi.c.

Change-Id: I811e8bd2be68813321dc4581af02e1c21b0da076
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/19910
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
4 files changed