drm/i915: extend the fsb_freq initialization to more platforms

drm/i915: extend the fsb_freq initialization to more platforms

Initialize fsb frequency for more platforms to be able to use it for GT
clock and rawclk frequency initialization.

Note: There's a discrepancy between existing pnv_fsb_freq() and
i9xx_hrawclk() regarding CLKCFG interpretation. Presume all PNV is
mobile.

Default to 1333 MHz for unknown values, similar to i9xx_hrawclk().

v2:
- Add MISSING_CASE() (Ville)
- Default to the same frequency for both branches (Ville)

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7cd6dbd4dafb900ac1dd12be0ec096ff1d5fc6cf.1718356614.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>