drm/i915/bxt: Fix HDMI DPLL configuration

a277ca7d should've been a no-functional-change commit, but it
removed the initialization of the dpll_hw_state for HDMI outputs,
resulting in state mismatches and a failed modeset with blank
screen. Fix this by reinstating the dpll_hw_state initialization.

v2:
- Make bxt_ddi_hdmi_set_dpll_hw_state() static.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Cc: Durgadoss R <durgadoss.r@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Fixes: a277ca7d ("drm/i915: Split bxt_ddi_pll_select()")
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1474901671-22719-1-git-send-email-imre.deak@intel.com