OMAP3: drop CONFIG_SPL_OS_BOOT_KEY and use local define

CONFIG_SPL_OS_BOOT_KEY is used only in board files. It is
not required to have a general CONFIG_ option. Rename it and
define it in board directory.

Signed-off-by: Stefano Babic <sbabic@denx.de>
Reviewed-by: Tom Rini <trini@ti.com>
diff --git a/board/timll/devkit8000/devkit8000.h b/board/timll/devkit8000/devkit8000.h
index aa69e6c..c1965e2 100644
--- a/board/timll/devkit8000/devkit8000.h
+++ b/board/timll/devkit8000/devkit8000.h
@@ -32,6 +32,9 @@
 	"NAND",
 };
 
+/* GPIO used to select between U-Boot and kernel */
+#define SPL_OS_BOOT_KEY	26
+
 /*
  * IEN  - Input Enable
  * IDIS - Input Disable