NAND boot: MPC8313ERDB support

Note that with older board revisions, NAND boot may only work after a
power-on reset, and not after a warm reset.  I don't have a newer board
to test on; if you have a board with a 33MHz crystal, please let me know
if it works after a warm reset.

Signed-off-by: Scott Wood <scottwood@freescale.com>
diff --git a/board/freescale/mpc8313erdb/config.mk b/board/freescale/mpc8313erdb/config.mk
index f768264..fd72a14 100644
--- a/board/freescale/mpc8313erdb/config.mk
+++ b/board/freescale/mpc8313erdb/config.mk
@@ -1 +1,7 @@
+ifndef NAND_SPL
+sinclude $(OBJTREE)/board/$(BOARDDIR)/config.tmp
+endif
+
+ifndef TEXT_BASE
 TEXT_BASE = 0xFE000000
+endif