tests: use drmtest_skip to check for rings

To simplify things add a set of gem_check_<ring> functions which take
care of this. Since I've opted for static inlines drmtest.h grew a few
more header includes which was a neat opportunity to dump a few redundant
#defines.

This kills all the skipped_all hand-rolled logic we have.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

tests/gem_write_read_ring_switch.c

@@ -151,11 +151,11 @@ static int has_ring(int ring)
 {
 	switch (ring) {
 	case I915_EXEC_RENDER: /* test only makes sense with separate blitter */
-		return HAS_BLT_RING(intel_get_drm_devid(fd));
+		return gem_check_blt(fd);
 	case I915_EXEC_BSD:
-		return HAS_BSD_RING(intel_get_drm_devid(fd));
+		return gem_check_bsd(fd);
 	case LOCAL_I915_EXEC_VEBOX:
-		return gem_has_vebox(fd);
+		return gem_check_vebox(fd);
 	default:
 		return 0;
 	}