sandybridge boards: Factor out MAX_CPUS

Also update autoport accordingly.

Change-Id: I12481363cf0e7afc54e2e339504f70632e8d72e2
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41839
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/intel/model_206ax/Kconfig

@@ -34,4 +34,8 @@ config IED_REGION_SIZE
 	hex
 	default 0x400000
 
+config MAX_CPUS
+	int
+	default 8
+
 endif