pineview boards: Factor out MAX_CPUS

Pineview has at most 4 threads.

Change-Id: I0f45f002d0bab0345bc061ac3c7a29237a536cc5
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41843
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/intel/socket_FCBGA559/Kconfig

@@ -27,4 +27,8 @@ config DCACHE_BSP_STACK_SIZE
 	  The amount of anticipated stack usage in CAR by bootblock and
 	  other stages.
 
+config MAX_CPUS
+	int
+	default 4
+
 endif