drm/bridge: dw-hdmi: Add SCDC and TMDS Scrambling support

Add support for SCDC Setup for TMDS Clock > 3.4GHz and enable TMDS
Scrambling when supported or mandatory.

This patch also adds an helper to setup the control bit to support
the high TMDS Bit Period/TMDS Clock-Period Ratio as required with
TMDS Clock > 3.4GHz for HDMI2.0 3840x2160@60/50 modes.

These changes were based on work done by Huicong Xu <xhc@rock-chips.com>
and Nickey Yang <nickey.yang@rock-chips.com> to support HDMI2.0 modes
on the Rockchip 4.4 BSP kernel at [1]

[1] https://github.com/rockchip-linux/kernel/tree/release-4.4

Cc: Nickey Yang <nickey.yang@rock-chips.com>
Cc: Huicong Xu <xhc@rock-chips.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1549022873-40549-2-git-send-email-narmstrong@baylibre.com

drivers/gpu/drm/bridge/synopsys/dw-hdmi.h

@@ -255,6 +255,7 @@
 #define HDMI_FC_MASK2                           0x10DA
 #define HDMI_FC_POL2                            0x10DB
 #define HDMI_FC_PRCONF                          0x10E0
+#define HDMI_FC_SCRAMBLER_CTRL                  0x10E1
 
 #define HDMI_FC_GMD_STAT                        0x1100
 #define HDMI_FC_GMD_EN                          0x1101