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/pxa255_idp.h b/include/configs/pxa255_idp.h
index cd95081..620d270 100644
--- a/include/configs/pxa255_idp.h
+++ b/include/configs/pxa255_idp.h
@@ -64,7 +64,7 @@
 
 #define CONFIG_MMC		1
 #define CONFIG_DOS_PARTITION	1
-#define BOARD_LATE_INIT		1
+#define CONFIG_BOARD_LATE_INIT
 
 #undef CONFIG_USE_IRQ			/* we don't need IRQ/FIQ stuff */