drm/pl111: Deprecate the pads from the DT binding

The pads were an earlier workaround for the internal image
pipeline in the Linux fbdev subsystem. As we move to generic
definition of display properties and drivers that no longer
need this to work, deprecate this property.

Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Liviu Dudau <Liviu.Dudau@arm.com>
Cc: devicetree@vger.kernel.org
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190724134959.2365-1-linus.walleij@linaro.org