Move select MMCONF_SUPPORT under northbridge

Move/remove MMCONF_SUPPORT reference under mainboard Kconfig, as
that feature originates from northbridge and cannot be disabled
for a single mainboard.

Change-Id: I6d6861079876ddddaff90b10f18edb6936e93bd0
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/3589
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/iwave/iWRainbowG6/Kconfig

@@ -9,7 +9,6 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select SOUTHBRIDGE_INTEL_SCH
 	select HAVE_PIRQ_TABLE
 #	select HAVE_MP_TABLE
-	select MMCONF_SUPPORT
 	select USE_PRINTK_IN_CAR
 	select UDELAY_LAPIC
 	select HAVE_ACPI_TABLES