gm45 boards: Factor out MAX_CPUS

The gm45 northbridge supports at most 4 threads. However, the only two
mobile Core 2 Quad models are not BGA956, so account for that as well.

Change-Id: Ie198ac4c366ec0bd53ddb337b6f9c03c331c73f5
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41844
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
diff --git a/src/cpu/intel/socket_BGA956/Kconfig b/src/cpu/intel/socket_BGA956/Kconfig
index eef81d5..638653c 100644
--- a/src/cpu/intel/socket_BGA956/Kconfig
+++ b/src/cpu/intel/socket_BGA956/Kconfig
@@ -18,4 +18,8 @@
 	hex
 	default 0x2000
 
+config MAX_CPUS
+	int
+	default 2
+
 endif