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/board/st-ericsson/u8500/u8500_href.c b/board/st-ericsson/u8500/u8500_href.c
index 9283fab..5f85fdc 100644
--- a/board/st-ericsson/u8500/u8500_href.c
+++ b/board/st-ericsson/u8500/u8500_href.c
@@ -226,7 +226,7 @@
 	0xA03FE024, 0x00000000	/* USB */
 };
 
-#ifdef BOARD_LATE_INIT
+#ifdef CONFIG_BOARD_LATE_INIT
 #ifdef CONFIG_MMC
 
 #define LDO_VAUX3_MASK		0x3
@@ -351,7 +351,7 @@
 
 	return 0;
 }
-#endif /* BOARD_LATE_INIT */
+#endif /* CONFIG_BOARD_LATE_INIT */
 
 static void early_gpio_setup(struct gpio_register *gpio_reg, u32 bits)
 {