dt-bindings: i2c: imx-lpi2c: Fix i.MX 8QXP compatible matching

The i.MX 8QXP DTSes use two compatibles so update the binding to fix
dtbs_check warnings like:

  arch/arm64/boot/dts/freescale/imx8qxp-mek.dt.yaml: i2c@5a820000:
    compatible: ['fsl,imx8qxp-lpi2c', 'fsl,imx7ulp-lpi2c'] is too long

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>