drm/i915: Index the ring frequency table by HW frequency range

When reporting the frequency table stored in the punit, report the full
range and not just the user restricted frequency range. In the process
keep the code to set the frequency table and read it the same.

v3: As we haven't separated the sb_lock from the pcu_lock yet, there's a
cycle between the pcu_lock and intel_runtime_pm_get.

References: f936ec34 ("drm/i915/skl: Updated the i915_ring_freq_table debugfs function")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> #v1
Link: https://patchwork.freedesktop.org/patch/msgid/20180308142648.4016-2-chris@chris-wilson.co.uk