freedreno: remove blit_via_copy_region()

freedreno: remove blit_via_copy_region()

If we hit the memcpy() path for copy_region(), that will try to do a
transfer_map(), which goes badly for blits to/from staging triggered
by transfer_map() or transfer_unmap().

We could possibly add fd_blit2() which has allow_transfer_map param,
and call that for staging blits.  But I'm not really sure if trying
the blit via copy_region() is very useful.  At least for newer gens
that implement fd_context::blit(), it probably isn't.

Signed-off-by: Rob Clark <robdclark@gmail.com>