net: phy: dp83867: add workaround for incorrect RX_CTRL pin strap

The data manual for DP83867IR/CR, SNLS484E[1], revised march 2017,
advises that strapping RX_DV/RX_CTRL pin in mode 1 and 2 is not
supported (see note below Table 5 (4-Level Strap Pins)).

It further advises that if a board has this pin strapped in mode 1 and
mode 2, then bit[7] of Configuration Register 4 (address 0x0031) must
be cleared to 0. This is to ensure proper operation of PHY.

Since it is not possible to detect in software if RX_DV/RX_CTRL pin is
incorrectly strapped, add a device-tree property to advertise this and
allow corrective action in software.
[1] http://www.ti.com/lit/ds/snls484e/snls484e.pdf



Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Reviewed-by: Hannes Schmelzer <oe5hpm@oevsv.at>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Tested-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>