Add option to use -Og

This adds support for using -Og when building U-Boot. According to the
gcc man page:

> -Og should be the optimization level of choice for the standard
> edit-compile-debug cycle, offering a reasonable level of optimization
> while maintaining fast compilation and a good debugging experience.

This optimization level is roughly -O1 minus a few additional
optimizations. It provides a noticably better debugging experience, with
many fewer variables <optimized out>.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/Kconfig b/Kconfig
index 8159c59..1127454 100644
--- a/Kconfig
+++ b/Kconfig
@@ -90,6 +90,12 @@
 	  Enabling this option will pass "-O2" to gcc, resulting in a faster
 	  U-Boot image.
 
+config CC_OPTIMIZE_FOR_DEBUG
+	bool "Optimize for debugging"
+	help
+	  Enabling this option will pass "-Og" to gcc, enabling optimizations
+	  which don't interfere with debugging.
+
 endchoice
 
 config OPTIMIZE_INLINING