gpio/crystalcove: Add additional GPIO for Panel control

Export PANEL_EN/DISABLE (offset 0x52) as additional GPIO. Needed
by display driver to enable the DSI panel on BYT platform where
the Panel EN/Disable control is routed thorugh CRC PMIC

CC: Samuel Ortiz <sameo@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>