drm/rockchip: dw_hdmi: add basic rk3228 support

Like the RK3328, RK322x SoCs offer a Synopsis DesignWare HDMI transmitter
and an Innosilicon HDMI PHY.

Add a new dw_hdmi_plat_data struct, rk3228_hdmi_drv_data.
Assign a set of mostly generic rk3228_hdmi_phy_ops functions.
Add dw_hdmi_rk3228_setup_hpd() to enable the HDMI HPD and DDC lines.

Signed-off-by: Justin Swartz <justin.swartz@risingedge.co.za>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20190522224631.25164-1-justin.swartz@risingedge.co.za