arm: dts: imx6ull: add pinctrl defines

Add pinctrl defines for NXP i.MX 6ULL.
Since i.MX6ULL reuses some definitions of i.MX6UL,
also add i.MX6UL pinctrl defines from linux kernel commit (29b4817d401).

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefano Babic <sbabic@denx.de>