drm/bridge: analogix_dp: some rockchip chips need to flip REF_CLK bit setting

As vendor document indicate, when REF_CLK bit set 0, then DP
phy's REF_CLK should switch to 24M source clock.

But due to IC PHY layout mistaken, some chips need to flip this
bit(like RK3288), and unfortunately they didn't indicate in the
DP version register. That's why we have to make this little hack.

Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Reviewed-by: Tomasz Figa <tomasz.figa@chromium.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>

include/drm/bridge/analogix_dp.h

@@ -18,6 +18,11 @@ enum analogix_dp_devtype {
 	RK3288_DP,
 };
 
+static inline bool is_rockchip(enum analogix_dp_devtype type)
+{
+	return type == RK3288_DP;
+}
+
 struct analogix_dp_plat_data {
 	enum analogix_dp_devtype dev_type;
 	struct drm_panel *panel;