tests/gem_tiled_partial_pread/write: fixes

Astonishing how dense I sometimes am ...
- increase the bo size so that we don't have any round-up to next tile
  size areas (which the 2d blit go over, but the 1d pread/pwrite calls
  will notice).
- correctly set tiling bits when copying back to a linear buffer.
- read back through a tiled bo to avoid messing with swizzling.

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

tests/gem_cs_prefetch.c

@@ -87,7 +87,7 @@ static void exec(int fd, uint32_t handle)
 
 int main(int argc, char **argv)
 {
-	uint32_t batch_end[2] = {MI_BATCH_BUFFER_END};
+	uint32_t batch_end[4] = {MI_BATCH_BUFFER_END, 0, 0, 0};
 	int fd, i, ret;
 	uint64_t aper_size;
 	int count;