lint/kconfig_lint: Make sure all symbols have a type defined

Show an error if a symbol does not have a defined type.

This caused a problem of an undefined symbol in check_defaults, so
we just skip those symbols there as we can't verify the default pattern
without knowing the type.

Change-Id: I28711a77962e16f6fc89789400363edd0fdd0931
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/17345
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@googlemail.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/lint/kconfig_lint_README

@@ -89,6 +89,7 @@ Errors in Kconfig that are also caught by Kconfig itself:
   int in another location.
 - Type keywords (bool, int, hex, string) used outside of a config block.
 - Using a 'prompt' keyword not inside a config or choice block.
+- Symbols with no defined type.
 
 Errors in coreboot source files:
 - The IS_ENABLED macro is only valid for bool symbols.