ARM: dts: imx: imx7d add iomuxc lpsr device node

Add device tree node to support iomuxc-lpsr controller, fsl,input-sel
phandle allows to get input select register base address which is
shared from main iomuxc controller.

Signed-off-by: Adrian Alonso <aalonso@freescale.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>