gianfar: Fix stashing support

Stashing is only supported on the 85xx (e500-based) SoCs.  The 83xx and 86xx
chips don't have a proper cache for this.  U-Boot has been updated to add
stashing properties to the device tree nodes of gianfar devices on 85xx.  So
now we modify Linux to keep stashing off unless those properties are there.

Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/powerpc/dts-bindings/fsl/tsec.txt

@@ -56,6 +56,12 @@ Properties:
     hardware.
   - fsl,magic-packet : If present, indicates that the hardware supports
     waking up via magic packet.
+  - bd-stash : If present, indicates that the hardware supports stashing
+    buffer descriptors in the L2.
+  - rx-stash-len : Denotes the number of bytes of a received buffer to stash
+    in the L2.
+  - rx-stash-idx : Denotes the index of the first byte from the received
+    buffer to stash in the L2.
 
 Example:
 	ethernet@24000 {