ARM: dts: imx6q-apalis-eval: add carrier board 3.3V supply

Add the 3.3V main supply on the carrier board. Currently as a fixed
supply since not all consumer are modeled yet. This gets also rid of
some missing supply warnings.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>