drm/vc4: crtc: Move HVS channel init before the PV initialisation

In order to avoid stale pixels getting stuck in an intermediate FIFO
between the HVS and the pixelvalve on BCM2711, we need to configure the HVS
channel before the pixelvalve is reset and configured.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/9d7c5a03bc1a1e6d50f7b617cc2d8a46a4bbb7bc.1599120059.git-series.maxime@cerno.tech