DM9000: Add data bus-width auto detection.

DM9000: Add data bus-width auto detection.

The U-boot DM9000x driver contains a compile time bus-width definition for
the databus connected to the network controller.

This compile check makes the code unclear, inflexible and is unneccessary.
It can be asked to the network controller what its bus-width is by reading bits
6 and 7 of the interrupt status register.

The linux kernel already uses a runtime mechanism to determine this bus-width,
so the implementation below looks somewhat like that implementation.

This change has been tested with DM9000A, DM9000E, DM9000EP.

Signed-off-by: Remy Bohmer <linux@bohmer.net>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>