Merge kernel uapi/sound/asound.h and asequencer.h

Merge kernel uapi/sound/asound.h and asequencer.h

Instead of keeping modified asound.h and asequencer.h, copy the files
in the kernel include/uapi/sound as is, and give some renames for
avoiding conflicts with alsa-lib's definitions.

Some structs, unions and typedefs in asound.h and asequencer.h are
once renamed in local.h before inclusion, then renamed back again.

A bonus by this action is that some local codes don't have to refer to
sndrv_xxx any longer.  However, some codes like src/seq/seq.c need
explicit cast because of unavoidable conflicts of struct types.

Another significant change is that now snd_pcm_sw_params.period_event
field is removed.  Instead, try to access the last reserved field
internally.

Signed-off-by: Takashi Iwai <tiwai@suse.de>