cogl: Include DRM 4CC conversions into CoglPixelFormat
This is at the moment still part of both MetaRendererNative and MetaDmaBuf, which means duplicated effort in code sections only barely related to color formats. By doing this, we can keep more of the pixel format code together, which is more future-proof as we want to add support for new pixel formats (like YUV-based ones).
Edited by Niels De Graef