net: phy: dp83867: Add documentation for optional impedance control

Add documention of ti,min-output-impedance and ti,max-output-impedance
which can be used to correct MAC impedance mismatch using phy extended
registers.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed