post, memory test: add memory_post_test() to include file

This include is needed, if this memory test is used "outside"
from post code, for example booting with nand_spl, and using
this memory test before copying u-boot code to RAM and jumping
to it.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/include/post.h b/include/post.h
index 3f259b7..3d23d22 100644
--- a/include/post.h
+++ b/include/post.h
@@ -147,6 +147,7 @@
 extern struct post_test post_list[];
 extern unsigned int post_list_size;
 extern int post_hotkeys_pressed(void);
+extern int memory_post_test(int flags);
 
 /*
  *  If GCC is configured to use a version of GAS that supports