radv: Invalidate L2 for TRANSFER_WRITE barriers

radv: Invalidate L2 for TRANSFER_WRITE barriers

CP DMA and PKT3_WRITE_DATA (in CmdUpdateBuffer) don't (currently) write
through L2. Therefore, to make these writes visible to later accesses
we must invalidate L2 rather than just writing it back, to avoid the
possibility that stale data is read through L2.

Cc: "17.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Alex Smith <asmith@feralinteractive.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Dave Airlie <airlied@redhat.com>