rendercopy: Pass context to rendercopy functions

rendercopy does the batch buffer flush internally, so if we want
to use it with multiple contexts, we need to pass the context
in from caller.

v2: Modify rendercopy_gen8 as well

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

tests/gem_ctx_basic.c

@@ -84,7 +84,7 @@ static void *work(void *arg)
 
 		if (uncontexted) {
 			igt_assert(rendercopy);
-			rendercopy(batch, &src, 0, 0, 0, 0, &dst, 0, 0);
+			rendercopy(batch, NULL, &src, 0, 0, 0, 0, &dst, 0, 0);
 		} else {
 			int ret;
 			ret = drm_intel_bo_subdata(batch->bo, 0, 4096, batch->buffer);