[ALSA] sound/core/seq: move declarations of globally visible variables to proper headers

sound/core/seq: move declarations of globally visible variables to proper headers

Signed-off-by: Marcin Ślusarz <marcin.slusarz@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>