drm/vc4: hvs: Reset muxes at probe time

drm/vc4: hvs: Reset muxes at probe time

[ Upstream commit 8514e6b1f40319e31ac4aa3fbf606796786366c9 ]

By default, the HVS driver will force the HVS output 3 to be muxed to
the HVS channel 2. However, the Transposer can only be assigned to the
HVS channel 2, so whenever we try to use the writeback connector, we'll
mux its associated output (Output 2) to the channel 2.

This leads to both the output 2 and 3 feeding from the same channel,
which is explicitly discouraged in the documentation.

In order to avoid this, let's reset all the output muxes to their reset
value.

Fixes: 87ebcd42fb7b ("drm/vc4: crtc: Assign output to channel automatically")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20220328153659.2382206-2-maxime@cerno.tech
Signed-off-by: Sasha Levin <sashal@kernel.org>