Skylake deprecates the usage of PORT_CLK_SEL and we are advised to use
the new DPLL_CRTL2 for the DDI->PLL mapping.

v2: Modified as per review comments
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NSatheeshakrishna M <satheeshakrishna.m@intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>