arm64: dts: imx8qm: add conn ss support

The CONN SS of MX8QM is mostly the same as MX8QXP except it has one more
USB HSIC module support. So we can fully reuse the exist CONN SS dtsi.
Add <soc>-ss-conn.dtsi with compatible string updated according to
imx8-ss-conn.dtsi.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>