arch/x86: Add a choice for selecting normal/fallback cbfs prefix

Setting the cbfs prefix is prone to error. Therefore add a Kconfig
choice for 2 common values, fallback and normal, while still keeping
the ability to specify an arbitrary value.

Change-Id: I04222120bd1241c3b0996afa27dcc35ac42fbbc8
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35822
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/src/Kconfig b/src/Kconfig
index 8fcb3ae..4c71f28 100644
--- a/src/Kconfig
+++ b/src/Kconfig
@@ -37,9 +37,26 @@
 	help
 	  Select this to prompt to use to configure the prefix for cbfs files.
 
+choice
+	prompt "CBFS prefix to use"
+	depends on CONFIGURABLE_CBFS_PREFIX
+	default CBFS_PREFIX_FALLBACK
+
+config CBFS_PREFIX_FALLBACK
+	bool "fallback"
+
+config CBFS_PREFIX_NORMAL
+	bool "normal"
+
+config CBFS_PREFIX_DIY
+	bool "Define your own cbfs prefix"
+
+endchoice
+
 config CBFS_PREFIX
-	string "CBFS prefix to use" if CONFIGURABLE_CBFS_PREFIX
-	default "fallback"
+	string "CBFS prefix to use" if CBFS_PREFIX_DIY
+	default "fallback" if !CONFIGURABLE_CBFS_PREFIX || CBFS_PREFIX_FALLBACK
+	default "normal" if CBFS_PREFIX_NORMAL
 	help
 	  Select the prefix to all files put into the image. It's "fallback"
 	  by default, "normal" is a common alternative.