option: Turn CMOS option backend into choice

In order to add more option backends, transform the current CMOS option
backend into a Kconfig choice. Replace the `select` directives, as they
cannot be used with choice options.

Change-Id: Id3180e9991f0e763b4bae93a92d40668e7fc99bc
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/54728
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/Kconfig

@@ -120,6 +120,13 @@ config UTIL_GENPARSER
 
 	  Otherwise, say N to use the provided pregenerated scanner/parser.
 
+choice
+	prompt "Option backend to use"
+	default USE_OPTION_TABLE if NVRAMCUI_SECONDARY_PAYLOAD
+
+config OPTION_BACKEND_NONE
+	bool "None"
+
 config USE_OPTION_TABLE
 	bool "Use CMOS for configuration values"
 	depends on HAVE_OPTION_TABLE
@@ -127,6 +134,8 @@ config USE_OPTION_TABLE
 	  Enable this option if coreboot shall read options from the "CMOS"
 	  NVRAM instead of using hard-coded values.
 
+endchoice
+
 config STATIC_OPTION_TABLE
 	bool "Load default configuration values into CMOS on each boot"
 	depends on USE_OPTION_TABLE