drm/rockchip: Add reflection properties

Add the KMS plane rotation property to the DRM rockchip driver,
for SoCs RK3328, RK3368 and RK3399.

RK3288 only supports rotation at the display level (i.e. CRTC),
but for now we are only interested in plane rotation.

This commit only adds support for the value of reflect-y
and reflect-x (i.e. mirroring).

Note that y-mirroring is not compatible with YUV.

The following modetest commands would test this feature,
where 30 is the plane ID, and 49 = rotate_0 + relect_y + reflect_x.

X mirror:
modetest -s 43@33:1920x1080@XR24 -w 30:rotation:17

Y mirror:
modetest -s 43@33:1920x1080@XR24 -w 30:rotation:33

XY mirror:
modetest -s 43@33:1920x1080@XR24 -w 30:rotation:49

Signed-off-by: Daniele Castagna <dcastagna@chromium.org>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20190109185639.5093-4-ezequiel@collabora.com