tests: Use igt macros more

Often just folding together of the common if (cond) printf;
abort|igt_skip|igt_fail; pattern. But in a few cases I've ripped out
more since the igt macros will already print the condition and errno.

A few tests where more work (like ripping out return codes en masse)
is needed left as-is.

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

tests/gem_mmap_offset_exhaustion.c

@@ -59,11 +59,7 @@ create_and_map_bo(int fd)
 	handle = gem_create(fd, OBJECT_SIZE);
 
 	ptr = gem_mmap(fd, handle, OBJECT_SIZE, PROT_READ | PROT_WRITE);
-
-	if (!ptr) {
-		fprintf(stderr, "mmap failed\n");
-		igt_assert(ptr);
-	}
+	igt_assert(ptr);
 
 	/* touch it to force it into the gtt */
 	*ptr = 0;