drm/rockchip: vop: test for P{H,V}SYNC

When connected to the MIPI DSI output, we need to use N{H,V}SYNC for the
internal connection but these flags are meaningless for DSI panels.
Switch the test so that we do not set the P{H,V}SYNC bits unless the
mode requires it.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Mark Yao <mark.yao@rock-chips.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
[seanpaul resolved conflict using macros instead of hardcoded values]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20170224125506.21533-21-john@metanate.com