intel-gpu-tools: avoid include of cairo.h on Android builds

intel-gpu-tools: avoid include of cairo.h on Android builds

A recent commit means igt_debugfs.c now needs to include igt_kms.h,
which in turn includes igt_fb.h and hence cairo.h.
We need to avoid this inclusion of cairo.h when building for Android,
(until we have a cairo port) so I have added a #ifndef around it.

Signed-off-by: Tim Gore <tim.gore@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>