realtek: hog the GS1900-24E external IC reset line

realtek: hog the GS1900-24E external IC reset line

The GPIO line connecting to the reset signals of the GS1900-24E(A1)'s
external ICs (RTL8218B phys and RTL8231 expander) cannot be asserted by
the MDIO subsystem, as the reset is shared between busses.

To prevent users from accidentally asserting the reset line, a GPIO hog
is created to permanently de-assert the signal, reliably keeping the
phys and GPIO expanders on.

Tested-by: Simon Fischer <simi.fischa@gmail.com>
Signed-off-by: Sander Vanheule <sander@svanheule.net>
(cherry picked from commit ba57225066243b28d2802ea5c47313c97767150e)