cosmetic: s/BOARD_LATE_INIT/CONFIG_BOARD_LATE_INIT

This renames BOARD_LATE_INIT to CONFIG_BOARD_LATE_INIT.
Along the way it removes some leftover

 #define BOARD_LATE_INIT		1

and adds some basic documentation for board specific
callbacks in README.

Signed-off-by: Helmut Raiger <helmut.raiger@hale.at>
Acked-by: Stefano Babic <sbabic@denx.de>
diff --git a/include/configs/mx35pdk.h b/include/configs/mx35pdk.h
index 670e76d..6f42fc7 100644
--- a/include/configs/mx35pdk.h
+++ b/include/configs/mx35pdk.h
@@ -42,7 +42,7 @@
 #define CONFIG_SYS_64BIT_VSPRINTF
 
 #define CONFIG_BOARD_EARLY_INIT_F
-#define BOARD_LATE_INIT
+#define CONFIG_BOARD_LATE_INIT
 
 #define CONFIG_CMDLINE_TAG		/* enable passing of ATAGs */
 #define CONFIG_REVISION_TAG