net: dwc_eth_qos: Start DMA and MAC after tail pointers are initialized

net: dwc_eth_qos: Start DMA and MAC after tail pointers are initialized

The DesignWare Cores Ethernet Quality-of-Service databook state that
receive and transmit descriptor list address and also transmit and
receive tail pointer registers should be initialized before the receive
and transmit DMAs are started.

It also state to enable the MAC receiver only after the DMA is active.
Otherwise, received frames can fill the Rx FIFO and overflow.

Move the activation of receive and transmit DMA and MAC receiver until
after tail pointer registers have been initialized.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>