fdt: Add ft_system_setup() function for system device tree additions

Add an additional function for adding information to the device tree before
booting. This permits additions which are not board-specific.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>
Reviewed-by: Tom Rini <trini@ti.com>
diff --git a/README b/README
index 837dca0..bf3ec67 100644
--- a/README
+++ b/README
@@ -669,6 +669,13 @@
 		Board code has addition modification that it wants to make
 		to the flat device tree before handing it off to the kernel
 
+		CONFIG_OF_SYSTEM_SETUP
+
+		Other code has addition modification that it wants to make
+		to the flat device tree before handing it off to the kernel.
+		This causes ft_system_setup() to be called before booting
+		the kernel.
+
 		CONFIG_OF_BOOT_CPU
 
 		This define fills in the correct boot CPU in the boot
@@ -3407,7 +3414,7 @@
 		to 128 or 256, although it does not have to be power of 2).
 
 		default: 4096
-		
+
 		CONFIG_MTD_UBI_BEB_LIMIT
 		This option specifies the maximum bad physical eraseblocks UBI
 		expects on the MTD device (per 1024 eraseblocks). If the