drm/i915: Use literal representation of cdclk tables

The bspec lays out legal cdclk frequencies, PLL ratios, and CD2X
dividers in an easy-to-read table for most recent platforms.  We've been
translating the data from that table into platform-specific code logic,
but it's easy to overlook an area we need to update when adding new
cdclk values or enabling new platforms.  Let's just add a form of the
bspec table to the code and then adjust our functions to pull what they
need directly out of the table.

v2: Fix comparison when finding best cdclk.

v3: Another logic fix for calc_cdclk.

v4:
 - Use named initializers for cdclk tables. (Ville)
 - Include refclk as a field in the table instead of adding all three
   ratios for each entry. (Ville)
 - Terminate tables with an empty entry to avoid needing to store the
   table size. (Ville)
 - Don't try so hard to return reasonable values from our lookup
   functions if we get impossible inputs; just WARN and return 0.
   (Ville)
 - Keep a bxt_ prefix on the lookup functions since they're still only
   used on bxt+ for now.  We can rename them later if we extend this
   table-based approach back to older platforms.  (Ville)

v5:
 - Fix cnl table's ratios for 24mhz refclk. (Ville)
 - Don't miss the named initializers on the cnl table. (Ville)
 - Represent refclk in table as u16 rather than u32. (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190910161506.7158-1-matthew.d.roper@intel.com