net: ethernet: stmmac: change dma descriptors to __le32

The stmmac driver does not take into account the processor may be big
endian when writing the DMA descriptors. This causes the ethernet
interface not to be initialised correctly when running a big-endian
kernel. Change the descriptors for DMA to use __le32 and ensure they are
suitably swapped before writing. Tested successfully on the
Cubieboard2.

Signed-off-by: Michael Weiser <michael.weiser@gmx.de>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>