drm/i915: Pass intel_atomic_state around

Pass the whole intel_atomic_state to skl_build_pipe_wm()
and skl_allocate_pipe_ddb() so we can start to iterate
stuff containerd in the commit.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201106173042.7534-2-ville.syrjala@linux.intel.com