Declare recovery and developer modes outside ChromeOS

Move the implementation for recovery and developer modes from
vendorcode/google/chromes to lib/.

Change-Id: I33335fb282de2c7bc613dc58d6912c47f3b5c06c
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/4308
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/vendorcode/google/chromeos/Kconfig

@@ -26,6 +26,7 @@ config CHROMEOS
 	bool "Build for ChromeOS"
 	default y
 	select TPM
+	select BOOTMODE_STRAPS
 	help
 	  Enable ChromeOS specific features like the GPIO sub table in
 	  the coreboot table. NOTE: Enabling this option on an unsupported