ARM: mxs: Rename 'hog-gpios'

hog_pins is used to setup the pin functions, and it is not neccesarily used only
for GPIO pins, so use only 'hog' to describe a more generic term.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>