ARM: dts: imx6qdl-sr-som: add 3.3V vcc regulator

Add a 3.3V regulator for devices connected to the vcc_3v3 supply
signal on the microsom.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>