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The Allwinner A10/A13 display controller hardware is expected to
support negative coordinates of the top left corners of the layers.
But there is some bug either in the kernel driver or in the hardware,
which messes up the picture on screen when the Y coordinate is negative
for YUV layer. Negative X coordinates are not affected. RGB formats
are not affected too (no matter whether the RGB layer is scaled or not).

We fix this by just recalculating which part of the buffer in memory
corresponds to Y=0 on screen and adjust the input buffer settings.

Fixes https://github.com/ssvb/xf86-video-sunxifb/issues/16

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>