northbridge/intel/gm45/Kconfig: Remove IOMMU symbol choice

In the gm45 code, IOMMU is always selected to be enabled.  Instead
this patch removes the Kconfig symbol and its dependencies.  This leads
to the same effect without the need for the symbol.

The symbol is still used in the K8 code as it's not selected, simply
defaulted to being enabled, and one of the mainboards disables it.

Change-Id: Ibc5939cd1e297d497bf71b1787d852f7cc09a551
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: http://review.coreboot.org/11345
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/src/northbridge/intel/gm45/Makefile.inc b/src/northbridge/intel/gm45/Makefile.inc
index 4050296..8bb083a 100644
--- a/src/northbridge/intel/gm45/Makefile.inc
+++ b/src/northbridge/intel/gm45/Makefile.inc
@@ -31,7 +31,7 @@
 romstage-y += igd.c
 romstage-y += pm.c
 romstage-y += ram_calc.c
-romstage-$(CONFIG_IOMMU) += iommu.c
+romstage-y += iommu.c
 
 ramstage-y += acpi.c