drm/i915: fix wrong PLL debug messages.

LPT does have PCH refclk, but it's different form the IBX/CPT/PPT one
and doesn't use the same structs. It is wrong to have a message saying
that "LPT does not has PCH refclk" (sic). While at it, signal that we
only want this function on IBX/CPT/PPT by renaming it and adding a
WARN.

On HSW we also print "0 shared PLLs initialized", but we *do* have
shared PLLs on HSW (LCPLL, WRPLL, SPLL) and we *do* initialize them.
We just don't use "struct intel_shared_dpll". So remove the debug
message.

In the future we may want to rename all that "intel shared pll" code
to "ibx shared pll", but I'll leave this to another patch.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>