Kconfig: Make the SEPARATE_ROMSTAGE default configurable in other files

This also sets a good default in arch and vboot to have a separate
romstage when it makes sense.

Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Change-Id: I09ab5f8c79917bf93c9d5c9dfd157c652478b186
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80580
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>
Reviewed-by: Jérémy Compostella <jeremy.compostella@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/x86/Kconfig

@@ -251,8 +251,9 @@ config BOOTBLOCK_SIMPLE
 	bool "Always load fallback"
 
 config BOOTBLOCK_NORMAL
-	select CONFIGURABLE_CBFS_PREFIX
 	bool "Switch to normal if CMOS says so"
+	select CONFIGURABLE_CBFS_PREFIX
+	select SEPARATE_ROMSTAGE
 
 endchoice