drm/i915: move shared_dpll into the pipe config

With the big sed-job prep work done this is now really simple. With
the exception that we only assign the right shared dpll id in the
->mode_set callback but also depend upon the old one still being
around.

Until that mess is fixed up we need to jump through a few hoops to
keep the old value save.

v2: Kill the funny whitespace spotted by Chris.

v3: Move the shared_dpll pipe config fixup into this patch as noticed
by Ville. Also unconditionally set the shared_dpll with the current
one, since otherwise we won't handle direct pch port -> cpu edp
transitions correctly.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>