gpio: mxs: Remove netdev.h

The MXS certainly does not support any sort of networking in GPIO code,
remove the netdev.h header.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>