drm/meson: add size and alignment requirements for dumb buffers

The Amlogic SoCs Canvas buffers stride must be aligned on 64bytes
and overall size should be aligned on PAGE width.

Adds a custom dumb_create op to adds these requirements.

Fixes: bbbe775e

 ("drm: Add support for Amlogic Meson Graphic Controller")
Suggested-by: Sky Zhou <sky.zhou@amlogic.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Sky Zhou <sky.zhou@amlogic.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190408090137.2402-1-narmstrong@baylibre.com