ARM: dts: imx: Pass a label to the AIPS nodes

Pass a label to the AIPS nodes to make it easier to reference
it from other devicetree files.

Some i.MX dtsi files already describe labels for the AIPS nodes.

Make it available for all SoCs for consistency.

U-Boot, for example usually needs to access the AIPS node to
pass U-Boot-specific properties.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>