new at91_emac network driver (NET_MULTI api)

* add's at91_emac (AT91RM9200) network driver (NET_MULTI api)
* enable driver with CONFIG_DRIVER_AT91EMAC
* generic PHY initialization
* modify AT91RM9200 boards to use NET_MULTI driver
* the drivers has been tested with LXT971 Phy and DM9161 Phy at
  MII and RMII interface

Signed-off-by: Jens Scharsig <js_at_ng@scharsoft.de>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
23 files changed