Add a new method to write the contents of a framebuffer to a file
descriptor. This can be used to capture frames from writeback
connectors.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Add a Card::has_writeback() method to report if the card support
writeback connectors. Similarly to universal planes, add a
KMSXX_DISABLE_WRITEBACK_CONNECTORS environment variable to disable
enumeration of writeback connectors to avoid confusing existing code
that expects all connectors to model an output.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Add support for the RGB332, XRGB1555 and XRGB4444 formats to the
PixelFormat class, the Python API, and the drawing utilities.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Add support for the 6 planar YUV formats (YUV and YVU, combined with
420, 422 or 444 subsampling) to the PixelFormat class, the Python API,
and the drawing utilities.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Add support for the NV16 and NV61 pixel formats to the PixelFormat
class, the Python API, and the drawing utilities.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Several pixel formats defined in the C++ PixelFormat class are missing
from the Python API. Add them.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

The device minor number is needed to access the debugfs directory
corresponding to the device. Make it available to users through a
get_minor() method on the Card object.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>