test: spl: Add a test for NAND

Add a SPL test for the NAND load method. We use some different functions to
do the writing from the main test since things like nand_write_skip_bad
aren't available in SPL.

We disable BBT scanning, since scan_bbt is only populated when not in SPL.
We use nand_spl_loaders.c as it seems to be common to at least a few boards
already. However, we do not use nand_spl_simple.c because it would require
us to implement cmd_ctrl.  The various nand load functions are adapted from
omap_gpmc. However, they have been modified for simplicity/correctness.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
diff --git a/test/image/Makefile b/test/image/Makefile
index b302101..11ed257 100644
--- a/test/image/Makefile
+++ b/test/image/Makefile
@@ -4,6 +4,7 @@
 
 obj-y += spl_load.o
 obj-$(CONFIG_SPL_UT_LOAD_FS) += spl_load_fs.o
+obj-$(CONFIG_SPL_UT_LOAD_NAND) += spl_load_nand.o
 obj-$(CONFIG_SPL_UT_LOAD_NET) += spl_load_net.o
 obj-$(CONFIG_SPL_NOR_SUPPORT) += spl_load_nor.o
 obj-$(CONFIG_SPL_UT_LOAD_OS) += spl_load_os.o