linux-phytec-fsl

stmmac: make platform drivers depend on their associated SoC

There's not much point, except compile test, enabling the stmmac
platform drivers unless their actual SoC is enabled. They're not
useful without it.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>