rawmidi: Add rawmidi framing API

rawmidi: Add rawmidi framing API

Optionally, incoming rawmidi bytes can be put inside a frame of type
snd_rawmidi_framing_tstamp_t.
The main current benefit is that can enable in-kernel timestamping of
incoming bytes, and that timestamp is likely to be more precise than
what userspace can offer.

Tstamp type framing requires a kernel >= 5.14 and a buffer size that
is a multiple of sizeof(snd_rawmidi_framing_tstamp_t). It is only
available on input streams.

Signed-off-by: David Henningsson <coding@diwic.se>
Signed-off-by: Takashi Iwai <tiwai@suse.de>