drm/i915: Manage HSW/BDW LCPLLs with the shared dpll interface

Manage the LCPLLs used with DisplayPort, so that all the HSW/BDW DPLLs
are managed by the shared dpll code.

v2: Introduce INTEL_DPLL_ALWAYS_ON flag to please state checker. (Ander)

v3: Initialize pll->flags in intel_shared_dpll_init(). (Ander)

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1457451987-17466-13-git-send-email-ander.conselvan.de.oliveira@intel.com