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/r2dplus.h b/include/configs/r2dplus.h
index a7a92f7..0ce3fa8 100644
--- a/include/configs/r2dplus.h
+++ b/include/configs/r2dplus.h
@@ -30,7 +30,7 @@
 #define CONFIG_SCIF_CONSOLE	1
 #define CONFIG_BAUDRATE		115200
 #define CONFIG_CONS_SCIF1	1
-#define BOARD_LATE_INIT		1
+#define CONFIG_BOARD_LATE_INIT
 
 #define CONFIG_BOOTDELAY	-1
 #define CONFIG_BOOTARGS		"console=ttySC0,115200"