arm64: dts: imx91: add i.MX91 dtsi support

arm64: dts: imx91: add i.MX91 dtsi support

The i.MX 91 family features an Arm Cortex-A55 running at up to 1.4GHz,
support for modern LPDDR4 memory to enable platform longevity, along
with a rich set of peripherals targeting medical, industrial and
consumer IoT market segments.

The mainly difference between i.MX91 and i.MX93 is as follows:
- i.MX91 removed some clocks and modified the names of some clocks.
- i.MX91 only has one A core.
- i.MX91 has different pinmux.

Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Joy Zou <joy.zou@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>