ARM: dts: imx7: Add "LPSR" to LPSR iomux pin names

The i.MX7 has two iomux controllers. the iomuxc and the iomuxc_lpsr.
In a board dts we have to make sure that both controllers are supplied
with the correct pins. It's way too easy to do this wrong since only
a look into the reference manual can reveal which pins belong to which
controller. To make this clearer add "LPSR" to the pin names which
belong to the LPSR controller.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>