snd_hdac_bus_queue_event() and snd_hdac_bus_exec_verb() are used only
internally in HD-audio core.  Let's drop the exports and move the
declarations into local.h.

Link: https://lore.kernel.org/r/20200516062854.22141-3-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>