drm/tegra: dc: rgb: Move PCLK shifter programming to CRTC

Asus TF700T tablet uses TC358768 DPI->DSI bridge that sits between Tegra's
DPI output and display panel input. Bridge requires to have stable PCLK
output before RGB encoder is enabled because it uses PCLK by itself to
clock internal logic and bridge is programmed before Tegra's encoder is
enabled. Hence the PCLK clock shifter must be programmed when CRTC is
enabled, otherwise clock is unstable and bridge hangs because of it.
Move the shifter programming from RGB encoder into CRTC.

Tested-by: Maxim Schwalm <maxim.schwalm@gmail.com> #TF700T
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>