This commit adds PCM functionality to transmit/receive PCM frames on
isochronous packet streaming. This commit enables userspace applications
to start/stop packet streaming via ALSA PCM interface.

Sampling rate requested by applications is used as sampling transmission
frequency of IEC 61883-1/6packet streaming. As I described in followed
commits, units in this series manages sampling clock frequency
independently of sampling transmission frequency, and they supports
resampling between their packet streaming/data block processing layer and
sampling data processing layer. This commit take this driver to utilize
these features for usability.

When internal clock is selected as source signal of sampling clock, this
driver allows user space applications to start PCM substreams at any rate
which packet streaming engine supports as sampling transmission frequency.
In this case, this driver expects units to perform resampling PCM frames
for rx/tx packets when sampling clock frequency and sampling transmission
frequency are mismatched. This is for daily use cases.

When any external clock is selected as the source signal, this driver
gets configured sampling rate from units, then restricts available
sampling rate to the rate for PCM applications. This is for studio use
cases.

Models in this series supports 64.0/128.0 kHz of sampling rate, however
these frequencies are not supported by IEC 61883-6 as sampling transmission
frequency. Therefore, packet streaming engine of ALSA firewire stack can't
handle them. When units are configured to use any external clock as source
signal of sampling clock and one of these unsupported rate is configured
as rate of the sampling clock, this driver returns EIO to user space
applications.

Anyway, this driver doesn't voluntarily configure parameters of sampling
clock. It's better for users to work with appropriate user space
implementations to configure the parameters in advance of usage.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>