mesa: move GL_APPLE_object_purgeable functions to new file

Move this code out of bufferobj.c since it's not strongly connected to
buffer objects.

Acked-by: Matt Turner <mattst88@gmail.com>

src/mapi/glapi/gen/gl_genexec.py

@@ -88,6 +88,7 @@ header = """/**
 #include "main/matrix.h"
 #include "main/multisample.h"
 #include "main/objectlabel.h"
+#include "main/objectpurge.h"
 #include "main/performance_monitor.h"
 #include "main/pipelineobj.h"
 #include "main/pixel.h"