drm/bridge: dw-hdmi-i2s: enable lpcm multi channels

Properly setup the channel count and layout in dw-hdmi i2s driver so
we are not limited to 2 channels.

Also correct the maximum channel reported by the DAI from 6 to 8 ch

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/20190812120726.1528-5-jbrunet@baylibre.com