Update the comments for context and surface
Update the comments for context and surface

Remove the limitation that a surface can't be shared between different
contexts at the same time.

Signed-off-by: Xiang, Haihao <8d677183e5993577d4fa73a419b76987913292d6@intel.com>

01org/libva-cros,01org/libva-cros,01org/libva-cros