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/zipitz2.h b/include/configs/zipitz2.h
index ade40b5..9505007 100644
--- a/include/configs/zipitz2.h
+++ b/include/configs/zipitz2.h
@@ -29,7 +29,7 @@
 #define	CONFIG_ZIPITZ2		1	/* Zipit Z2 board */
 #define	CONFIG_SYS_TEXT_BASE	0x0
 
-#undef	BOARD_LATE_INIT
+#undef	CONFIG_BOARD_LATE_INIT
 #undef	CONFIG_USE_IRQ
 #undef	CONFIG_SKIP_LOWLEVEL_INIT