drm/bridge: dw-hdmi-i2s: enable only the required i2s lanes

Enable the i2s lanes depending on the number of channel in the stream

Reviewed-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190812120726.1528-8-jbrunet@baylibre.com