drm/i915: Allow PCH DPLL sharing regardless of DPLL_SDVO_HIGH_SPEED

drm/i915: Allow PCH DPLL sharing regardless of DPLL_SDVO_HIGH_SPEED

DPLL_SDVO_HIGH_SPEED must be set for SDVO/HDMI/DP, but nowhere is it
forbidden to set it for LVDS/CRT as well. So let's also set it on
CRT to make it possible to share the DPLL between HDMI and CRT.

What that bit apparently does is enable the x5 clock to the port,
which then pumps out the bits on both edges of the clock. The DAC
doesn't need that clock since it's not pumping out bits, but I don't
think it hurts to have the DPLL output that clock anyway.

This is fairly important on IVB since it has only two DPLLs with three
pipes. So trying to drive three or more PCH ports with three pipes
is only possible when at least one of the DPLLs gets shared between
two of the pipes.

SNB doesn't really need to do this since it has only two pipes. It could
be done to avoid enabling the second DPLL at all in certain cases, but
I'm not sure that's such a huge win. So let's not do it for SNB, at
least for now. On ILK it never makes sense as the DPLLs can't be shared.

v2: Just always enable the high speed clock to keep things simple (Daniel)
    Beef up the commit message a bit (Daniel)

Cc: Nick Yamane <nick.diego@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Tested-by: Nick Yamane <nick.diego@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97204
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474878646-17711-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
(cherry picked from commit 7d7f8633a82763577727762ff3ac1df3017cb8fe)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>