i945 boards: Factor out MAX_CPUS

At least one mobile 945 series northbridge supports 4 threads, because
the dual-core Atom 330 CPU supports Hyper-threading. Therefore, we use
that as the default for this chipset.

Change-Id: I899ed1644d9b2da4fc72f09233a421200770110d
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41845
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/intel/d945gclf/Kconfig

@@ -31,8 +31,4 @@ config IRQ_SLOT_COUNT
 	int
 	default 18
 
-config MAX_CPUS
-	int
-	default 4
-
 endif # BOARD_INTEL_D945GCLF