drm/rockchip: dw-mipi-dsi: ensure PHY is reset

Also don't power up the DSI host at this point since this is not
necessary in order to configure the PHY and we do so later when
selecting video or command mode.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Chris Zhong <zyw@rock-chips.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170224125506.21533-15-john@metanate.com