net: qcom/emac: enforce DMA address restrictions

The EMAC has a restriction that the upper 32 bits of the base addresses
for the RFD and RRD rings must be the same.  The ensure that restriction,
we allocate twice the space for the RRD and locate it at an appropriate
address.

We also re-arrange the allocations so that invalid addresses are even
less likely.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>