drm/i915: Add a local pipe variable to vlv_enable_pll()

Avoid redundant crtc->pipe lookups by giving vlv_enable_pll() a local
pipe variable. Also makes it look more like the corresponding CHV code.

While at is change the CHV code to enum pipe from int,

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1458052809-23426-5-git-send-email-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>