ARM: sti: stih416: Add support for B2020 RevE

The B2020 RevE differs from the other B2020 boards in a few subtle ways;
including the Ethernet reset GPIO which this patch adds support for and
the LED wiring which will follow in a latter patch.  Without supplying
these differences Ethernet and the board LEDs simply will not work.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>