drm/i915/skl+: Remove minimum block allocation from crtc state.

This is not required any more now that we get fresh state from
drm_atomic_crtc_state_for_each_plane_state. Zero all state
in advance.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1477489299-25777-6-git-send-email-maarten.lankhorst@linux.intel.com