board/freescale:Remove use of CONFIG_SPL_NAND_MINIMAL

CONFIG_SPL_NAND_MINIMAL should not be used as it was defined for temporary
review purpose.

So, use CONFIG_SPL_NAND_BOOT config.

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>
diff --git a/README b/README
index 895fef3..e58e9c0 100644
--- a/README
+++ b/README
@@ -3267,6 +3267,9 @@
 		Defines the size and behavior of the NAND that SPL uses
 		to read U-Boot
 
+		CONFIG_SPL_NAND_BOOT
+		Add support NAND boot
+
 		CONFIG_SYS_NAND_U_BOOT_OFFS
 		Location in NAND to read U-Boot from