mb/lenovo/t400: Increase MAX_CPUS to 4

The Lenovo T400 has a CPU socket that can fit quad cores.

Change-Id: I585775ac9510cc7d2c2d731531f536c1a56b81e8
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/18059
Tested-by: build bot (Jenkins)
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/mainboard/lenovo/t400/Kconfig

@@ -46,7 +46,7 @@ config USBDEBUG_HCD_INDEX
 
 config MAX_CPUS
 	int
-	default 2
+	default 4
 
 config CBFS_SIZE
 	hex