drm/i915: kill intel_ddi_pll_select()

All it does is pick the encoder and call intel_get_shared_dpll(). We
can just do this in the caller. One less indirection level during code
reading.

As another plus, now the two callers of intel_get_shared_dpll() are
{ironlake,haswell}_crtc_compute_clock().

Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1490209125-20046-2-git-send-email-paulo.r.zanoni@intel.com