arrandale boards: Factor out MAX_CPUS

Arrandale CPUs have at most 4 threads.

Change-Id: Ifecbf5583011ff5e36c576d582a6276bc9b72803
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41840
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/intel/model_2065x/Kconfig

@@ -29,4 +29,8 @@ config SMM_RESERVED_SIZE
 	hex
 	default 0x100000
 
+config MAX_CPUS
+	int
+	default 4
+
 endif