arm64: dts: imx8mm-evk: add vcc supply for pca6416

pca6146 requires vcc-supply to work on i.MX8MM-EVK board.

Reviewed-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Signed-off-by: Adrian Alonso <adrian.alonso@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>