spl, nand: add option to boot raw u-boot.bin image only

enable to boot only a raw u-boot.bin image from nand with the
CONFIG_SPL_NAND_RAW_ONLY define. This option saves space on
boards where spl space is low.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Andreas Bießmann <andreas.devel@googlemail.com>
Reviewed-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/README b/README
index c3a9dfc..837dca0 100644
--- a/README
+++ b/README
@@ -3605,6 +3605,10 @@
 		Support for the MTD subsystem within SPL.  Useful for
 		environment on NAND support within SPL.
 
+		CONFIG_SPL_NAND_RAW_ONLY
+		Support to boot only raw u-boot.bin images. Use this only
+		if you need to save space.
+
 		CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT
 		Set for the SPL on PPC mpc8xxx targets, support for
 		drivers/ddr/fsl/libddr.o in SPL binary.