drivers: net: xgene: Fix module unload crash - change sw sequence

When the driver is configured as kernel module and when it gets
unloaded and reloaded, kernel crash was observed.  This patch
addresses the software cleanup by doing the following,

- Moved register_netdev call after hardware is ready
- Since ndev is not ready, added set_irq_name to set irq name
- Since ndev is not ready, changed mdio_bus->parent to pdev->dev
- Replaced netif_start(stop)_queue by netif_tx_start(stop)_queues
- Removed napi_del call since it's called by free_netdev
- Added dev_close call, within remove
- Added shutdown callback
- Changed to use dmam_ APIs

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Tested-by: Fushen Chen <fchen@apm.com>
Tested-by: Toan Le <toanle@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>