post: Migrate to Kconfig

We move the existing CONFIG_POST_* functionality over to CFG_POST and
then introduce CONFIG_POST to Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.fsl-ddr b/doc/README.fsl-ddr
index cec5d94..10e63f3 100644
--- a/doc/README.fsl-ddr
+++ b/doc/README.fsl-ddr
@@ -137,7 +137,7 @@
 2. Memory test can be done with Power-On-Self-Test function, activated at
    compile time.
 
-   In order to enable the POST memory test, CONFIG_POST needs to be
+   In order to enable the POST memory test, CFG_POST needs to be
    defined in board configuraiton header file. By default, POST memory test
    performs a fast test. A slow test can be enabled by changing the flag at
    compiling time. To test memory bigger than 2GB, 36BIT support is needed.