ARM: dts: imx6-tx6: remove container node around pinctrl nodes

Remove the function node around the pinctrl nodes that was obsoleted
by commit 5fcdf6a7 ("pinctrl: imx: Allow parsing DT without
function nodes"), we can save this container node.

Also move the iomux node to the bottom of the file to improve
readability of the file.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>