drm/i915: sanitize suspend/resume helper function names

By now the S4 freeze/thaw and S3 suspend/resume events are handled the
same way, so we can rename the freeze/thaw internal helpers to
suspend/resume accordingly to make clearer what the helpers do. Also
rename i915_resume_early to i915_drm_resume_early aligning it with the
rest of the helper names.

No functional change.

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