pci: Make HW.PCI.MMConf a public generic

GCC 8 wants us to tie the hidden, private state of HW.PCI.MMConf to a
surrounding state. Though, as it's impossible to do that before the
package instantiation, we can only comply by making it public.

Change-Id: I41c3d1324a7d9acde5be2c246011f976361e8f2b
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/26304
Tested-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/common/hw-pci-mmconf.ads b/common/hw-pci-mmconf.ads
index 03c9f44..597ebfa 100644
--- a/common/hw-pci-mmconf.ads
+++ b/common/hw-pci-mmconf.ads
@@ -17,7 +17,7 @@
 pragma Elaborate_All (HW.MMIO_Range);
-private generic
    Dev : Address := (0, 0, 0);
 package HW.PCI.MMConf