batch: Specify number of relocations to accommodate

Since relocations are variable size, depending upon generation, it is
easier to handle the resizing of the batch request inside the
BEGIN_BATCH macro. This still leaves us with having to resize commands
in a few places - which still need adaption for gen8+.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

tests/gem_bad_batch.c

@@ -48,7 +48,7 @@ struct intel_batchbuffer *batch;
 static void
 bad_batch(void)
 {
-	BEGIN_BATCH(2);
+	BEGIN_BATCH(2, 0);
 	OUT_BATCH(MI_BATCH_BUFFER_START);
 	OUT_BATCH(0);
 	ADVANCE_BATCH();