OMAP2: Devkit8000: Use _cansleep GPIO functions for displayreset lines

The display reset lines are connected to a TPS65930 which may sleep
when changing GPIO values. Use the appropriate function to silence
a nasty warning from gpiolib.

Signed-off-by: Daniel Morsing <daniel.morsing@gmail.com>
Acked-by: Thomas Weber <weber@corscience.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>