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/pleb2.h b/include/configs/pleb2.h
index 7dd6246..2aeb7fb 100644
--- a/include/configs/pleb2.h
+++ b/include/configs/pleb2.h
@@ -38,7 +38,7 @@
 #define CONFIG_PLEB2		1	/* on an PLEB2 Board	    */
 #undef CONFIG_LCD
 #undef CONFIG_MMC
-#define BOARD_LATE_INIT		1
+#define CONFIG_BOARD_LATE_INIT
 #define	CONFIG_SYS_TEXT_BASE	0x0
 
 #undef CONFIG_USE_IRQ			/* we don't need IRQ/FIQ stuff */