overo: add SPL support

* implementation based on ti beagleboard/omap3evm
* timing data and i2c workaround for revision 0 boards taken from x-loader
* run-tested with overo revision 0 and 1 / boot from NAND and SDcard
* run-tested with x-loader

Signed-off-by: Andreas Müller <schnitzeltony@gmx.de>
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/board/overo/overo.h b/board/overo/overo.h
index 915f15b..b41b628 100644
--- a/board/overo/overo.h
+++ b/board/overo/overo.h
@@ -33,6 +33,11 @@
 #endif
 };
 
+/* overo revisions */
+#define REVISION_0	0x0
+#define REVISION_1	0x1
+#define REVISION_2	0x2
+
 /*
  * IEN  - Input Enable
  * IDIS - Input Disable