Added comments to glamor_pixmap_create. To be refined in the future.
We need to identify whether a pixmap is a CPU memory pixmap or a
GPU pixmap. Current implementation is not correct. There are three
cases:
1. Too large pixmap, we direct it to CPU memory pixmap.
2. w ==0 || h == 0 pixmap, this case has two possibilities:
2.1 It will become a screen pixmap latter, then it should be
GPU type.
2.2 It's a scratch pixmap or created from a share memory, then
it should belong to CPU memory.
XXX, need to be refined latter.
b8ce483f58