nb/intel/nehalem: Start VBOOT in bootblock with a separate verstage

Tested on Lenovo Thinkpad X201, selects slot or recovery just fine.

Change-Id: Ia2b2f2b95510388599266264eaed0d64ce9b6ec5
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35952
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/northbridge/intel/nehalem/Kconfig

@@ -27,7 +27,8 @@ if NORTHBRIDGE_INTEL_NEHALEM
 
 config VBOOT
 	select VBOOT_MUST_REQUEST_DISPLAY
-	select VBOOT_STARTS_IN_ROMSTAGE
+	select VBOOT_STARTS_IN_BOOTBLOCK
+	select VBOOT_SEPARATE_VERSTAGE
 
 config MMCONF_BUS_NUMBER
 	int