espi: Add support for debug helper to print slave capabilities

This change adds a Kconfig option to enable eSPI debugging that pulls
in a helper function to print slave capabilities.

BUG=b:153675913

Signed-off-by: Furquan Shaikh <furquan@google.com>
Change-Id: I8ff250fe85dfa9370bf93ce3c7e2de5c069bf9e9
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41254
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/lib/Kconfig

@@ -75,3 +75,9 @@ config NO_FMAP_CACHE
 	  If your platform really doesn't want to use an FMAP cache (e.g. due to
 	  space constraints), you can select this to disable warnings and save
 	  a bit more code.
+
+config ESPI_DEBUG
+	bool
+	help
+	  This option enables eSPI library helper functions for displaying debug
+	  information.