we've got into a bit of a mess with how we name platform specific
symbols and files, so this is a first pass at trying to tidy that up.
All platform specific symbols should be named like
cogl_<platform>_symbol_name and similarly files should be named like
cogl-<platform>-filename.c
This patch tackles the X11 specific renderer/display APIs as a start.
Signed-off-by: Neil Roberts <neil@linux.intel.com>