image: Add CONFIG_FIT_SPL_PRINT to control FIT image printing in SPL

This code is very large, and in SPL it isn't always useful to print
out image information (in fact there might not even be a console
active). So disable this feature unless this option is set.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index defdedb..d832bcb 100644
--- a/README
+++ b/README
@@ -2997,6 +2997,12 @@
 		use an arch-specific makefile fragment instead, for
 		example if more than one image needs to be produced.
 
+		CONFIG_FIT_SPL_PRINT
+		Printing information about a FIT image adds quite a bit of
+		code to SPL. So this is normally disabled in SPL. Use this
+		option to re-enable it. This will affect the output of the
+		bootm command when booting a FIT image.
+
 Modem Support:
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