glut_waffle: Refactor some code into common.[ch]

This is in preparation for adding support for input to glut_waffle. Input
for each platform (X11, Wayland, etc) will be implemented in a separate
file. This patch moves common code needed for each platform from
glut_waffle.c into common.[ch].

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
5 files changed