drm/i915/adl_p: Program DP/HDMI link rate to DDI_BUF_CTL

On ADL_P besides programming the PLL accordingly the DP/HDMI link rate
should be also programmed to the DDI_BUF_CTL register, do that.

Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210519000625.3184321-16-lucas.demarchi@intel.com