powerpc/44x: Add more changes for APM821XX EMAC driver

This patch includes:

  Configure EMAC PHY clock source (clock from PHY or internal clock).

  Do not advertise PHY half duplex capability as APM821XX EMAC does not support half duplex mode.

  Add changes to support configuring jumbo frame for APM821XX EMAC.

[ Fix coding style -DaveM ]

Signed-off-by: Duc Dang <dhdang@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>