dp83640: Program pulsewidth2 values of perout triggers 0 and 1

Periodic output triggers 0 and 1 of the dp83640 has a programmable
duty-cycle which is controlled by the Pulsewidth2 field of the trigger
data register.  This field is not documented in the datasheet, but it
is described in the "PHYTER Software Development Guide" section
3.1.4.1. Failing to set the field can result in unstable/no trigger
output.

Add programming of the Pulsewidth2 field, setting it to the same value
as the Pulsewidth field for a 50% duty cycle.

Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Signed-off-by: David S. Miller <davem@davemloft.net>