cpuat91: unbreak ethernet

cpuat91: unbreak ethernet

* the following problems are met :
config was set to use the new driver as a default but
- RMII was not enabled for the new driver
- the new driver didn't compile with RMII enabled
- the new driver initialize a PHY at address O when the PHY of
this board is at 1 thus we get "AT91 EMAC RMII: No PHY present"

* to fix these problems, this patch :
- enable RMII for the new driver
- fix the wrong define used in the at91_emac.c
- allow the config file to set a default phy address (and use
0 as a default as in the actual at91_emac.c driver)

Signed-off-by: Eric Bénard <eric@eukrea.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>