ARM: dts: Use defined GPIO constants in flags cell for OMAP2+ boards

Many OMAP2+ DTS are not using the defined constants to express
the GPIO polarity. Replace these so the DTS are easier to read.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>