drm/i915: Introduce intel_dpll_get_hw_state()

Add a wrapper for the pll .get_hw_state() vfunc. Makes life
a bit less miserable when you don't have to worry where the
function pointer is stored.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201109231239.17002-1-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>