This adds support for Rockchip CVBS found on rk3328 Linux.
The CVBS driver is based on the DRM framework.
NTSC(720x480i60hz) and PAL(720x576i50hz) modes are supported.
it's worth noting that rk3328 CVBS dclk is base on hdmi clk,so hdmi
should be enabled.
Change-Id: I059808111bfa96724eb629b6fc37915a4852e234
Signed-off-by: algea.cao <algea.cao@rock-chips.com>