mtd: Add a CONFIG_SPL_MTD_SUPPORT for a more full NAND subsystem in SPL

This mainly converts the am335x_spl_bch driver to the "normal" format
which means a slight change to nand_info within the driver.

Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/README b/README
index 39e05d3..7b5d01b 100644
--- a/README
+++ b/README
@@ -3326,6 +3326,10 @@
 		Support for NAND boot using simple NAND drivers that
 		expose the cmd_ctrl() interface.
 
+		CONFIG_SPL_MTD_SUPPORT
+		Support for the MTD subsystem within SPL.  Useful for
+		environment on NAND support within SPL.
+
 		CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT
 		Set for the SPL on PPC mpc8xxx targets, support for
 		drivers/ddr/fsl/libddr.o in SPL binary.