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>
diff --git a/src/Kconfig b/src/Kconfig
index 2bcc3ce..2afb9db 100644
--- a/src/Kconfig
+++ b/src/Kconfig
@@ -245,7 +245,6 @@
 
 config SEPARATE_ROMSTAGE
 	bool "Build a separate romstage"
-	default y
 	help
 	  Build a separate romstage that is loaded by bootblock. With this
 	  option disabled the romstage sources are linked inside the bootblock
@@ -1538,3 +1537,6 @@
 	bool
 	default n if RAMPAYLOAD
 	default y
+
+config SEPARATE_ROMSTAGE
+	default y