drm: add Atmel HLCDC support

The Atmel HLCDC (High LCD Controller) IP provides at least one primary
plane and a configurable PWM that can be used to control a PWM backlight
device.

Depending on the IP version it might also provides one or several overlays
and an hardware cursor.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
ARM: aT91/dt: split sama5d3 lcd pin definitions to match RGB mode configs

The HLCDC (High LCD Controller) IP supports 4 different output mode
(RGB444, RGB565, RGB666 and RGB888) and the pin muxing depends on the
chosen RGB mode.

Split the pin definition to be able to set the pin config according to the
selected mode.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
ARM: at91/dt: define the HLCDC node on available sama5d3 boards

Define the HLCDC (High LCD Controller) IP available on some sama5d3 SoCs.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
ARM: at91/dt: add LCD panel description to sama5d3xdm.dtsi

Add LCD panel related nodes (backlight, regulators and panel) to the
sama5d3 Display Module dtsi.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
ARM: at91/dt: enable the LCD panel on the sama5d3ek board

Enable LCD related nodes and reference the panel node in the hlcdc (High
LCD Controller) controller.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>