dt-bindings: i2c: imx-lpi2c: Add imx8ulp compatible string

Add the compatible for i.MX8ULP.

Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>