ARM: dts: imx6qdl-sabresd: add light sensor support

Add isl29023 light sensor support on i2c3 bus, the light
sensor's power is controlled by a fixed regulator, since
the isl29023 driver and most of other sensors on same
board like mag3110 and mma8451 do NOT support regulator
operation currently, they are all controlled by this
regulator, so this patch also adds the fixed regulator
support and make it always on.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>