leds: pca963x: Add bindings to invert polarity

Add a new DT property, nxp,inverted-out, to invert the polarity
of the output.

Tested on PCA9634.

Signed-off-by: Anders Darander <anders@chargestorm.se>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>