nb/intel/gm45: Factor out {DMI,EP,MCH}BAR accessors

These accessors can be reused for several other northbridges.

Tested with BUILD_TIMELESS=1, Roda RK9 remains identical.

Change-Id: Ia16ccc63dddebf938f4e9a7f5518e4d25d3e7e66
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49748
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/Kconfig

@@ -523,6 +523,7 @@ comment "CPU"
 source "src/cpu/Kconfig"
 comment "Northbridge"
 source "src/northbridge/*/*/Kconfig"
+source "src/northbridge/*/*/Kconfig.common"
 comment "Southbridge"
 source "src/southbridge/*/*/Kconfig"
 comment "Super I/O"