drm/i915: Rename skl_vco_freq to cdclk_pll.vco

drm/i915: Rename skl_vco_freq to cdclk_pll.vco

We'll want to store the cdclk PLL (whatever PLL that is in reality) vco
frequency somewhere on other platforms too, so let's rename the
skl_vco_freq to cdclk_pll.vco, and let's store it in kHz instead of MHz
to match most of the other clocks.

v2: Drop the spurious > vs != change (Imre)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1463172100-24715-14-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>