dm9000: Implement full reset of DM9000 network device

A Davicom application note for the DM9000 network device recommends
performing software reset twice to correctly initialise the device.
Without this reset some devices fail to initialise correctly on
system startup.

Cc: David S. Miller <davem@davemloft.net>
Cc: Jingoo Han <jg1.han@samsung.com>
Cc: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Michael Abbott <michael.abbott@diamond.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>