drm/i915/adl_p: Add cdclk support for ADL-P

ADL-P has 3 possible refclk frequencies: 19.2MHz,
24MHz and 38.4MHz

While we're at it, remove the drm_WARNs.  They've never actually helped
us catch any problems, but it's very easy to forget to update them
properly for new platforms.

BSpec: 55409, 49208
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Clinton Taylor <clinton.a.taylor@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Clinton Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210514153711.2359617-9-matthew.d.roper@intel.com