ARM: dts: sun6i: Disable display pipeline by default

While we now support the internal display pipeline found on sun6i, it
is possible that we are unable to enable the display for some boards,
due to a lack of drivers for the panels or bridges found on them. If
the display pipeline is enabled, the driver will try to enable, and
possibly screw up the simple framebuffer U-boot had configured.

Disable the display pipeline by default.

Fixes: 6d0e5b70

 ("ARM: dts: sun6i: Add device nodes for first
		      display pipeline")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>