mxc_fec: fix some erroneous PHY accesses.

This patch fixes erroneous access to the ethernet PHY which broke the driver.
1. Selector field in the auto-negotiation register must be 0x00001 for
using 802.3, not 0x00000 which is reseved.
2. Access to the PHY address specified by CONFIG_FEC_MXC_PHYADDR, not
0x0 fixed address.

This has been tested in i.MX27 Litekit board and eldk-4.2 toolchains.

Now using proper defines for auto-negotiation register.

Signed-off-by: Javier Martin <javier.martin@vista-silicon.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>