freedreno: fix resource flushing confusion

freedreno: fix resource flushing confusion

A resource flush is an upload of a hypothetically-staging texture to the
GPU. For a UMA system, this will largely be a no-op or
cache-maintenance. Move the render flush logic into transfer_map where
it belongs, and clear out the transfer_flush function.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>