drm/i915: convert fsb_freq and mem_freq to kHz

drm/i915: convert fsb_freq and mem_freq to kHz

We'll want to use fsb frequency for deriving GT clock and rawclk
frequencies in the future. Increase the accuracy by converting to
kHz. Do the same for mem freq to be aligned.

Round the frequencies ending in 666 to 667.

v2: Also handle mem_freq in gen5_rps_init() (Ville)

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/17fe2544b876549f63fac0f956273f5f282081b3.1718356614.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>