drm/etnaviv: exec and MMU state is lost when resetting the GPU

commit 725cbc7884c37f3b4f1777bc1aea6432cded8ca5 upstream.

When the GPU is reset both the current exec state, as well as all MMU
state is lost. Move the driver side state tracking into the reset function
to keep hardware and software state from diverging.

Cc: stable@vger.kernel.org # 5.4
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Michael Walle <michael@walle.cc>
Tested-by: Marek Vasut <marex@denx.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>