ARM: dts: imx: ventana: cleanup pinctrl groups

Follow the conventions for pinctrl:
 - grouping pinctrl in logical alphabatized groups
 - remove any pinctrl not being used by a driver or needed by user
 - move iomuxc to bottom of file for readability

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>