dt-bindings: phy: dp83867: provide a workaround for incorrect RX_CTRL pin strap

dt-bindings: phy: dp83867: provide a 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 to ensure proper operation of the PHY, a software workaround
must be implemented.

Since it is not possible to detect in software if RX_DV/RX_CTRL pin is
incorrectly strapped, add a device-tree property for the board 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>
[nsekhar@ti.com: rebase to mainline, split documentation into separate patch]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>