panfrost: Use a hierarchy_mask of 0x0 for small fbs

For framebuffers smaller in any dimension than 16, we need to use a mask
of 0x0.

Make sure that we use a BO of TILER_MINIMUM_HEADER_SIZE when there's
draws on tiles smaller than 16 on any direction.

Use 0x41 as the default, so it also works on T720.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>