dts: arm: nxp_mcxn947: Add 'nxp,reference-cells' for vref node

Add new property 'nxp,reference-cells' for vref node.
Remove lpadc nodes 'nxp,reference-supply' property.
Add new property 'nxp,references' for lpadc nodes.

Signed-off-by: Zhaoxiang Jin <Zhaoxiang.Jin_1@nxp.com>