etnaviv: rework the stream flush to always go through the context flush

etnaviv: rework the stream flush to always go through the context flush

This way we can ensure that the pipe driver tracking of pending resources
stays in sync with the actual command buffer state, even if a space
reservation triggers a forced flush.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Jonathan Marek <jonathan@marek.ca>