ARM: iop32x: fix power off handling for the EM7210 board

This board was missed when converting all the others to proper
abstracted GPIO handling. Fix it up the right way by requesting
and driving GPIO line 0 high through gpiolib to power off the
machine.

Cc: Arnaud Patard <arnaud.patard@rtp-net.org>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>