Support for Blokas Labs pisound board

Support for Blokas Labs pisound board

Pisound dynamic overlay (#1760)

Restructuring pisound-overlay.dts, so it can be loaded and unloaded dynamically using dtoverlay.

Print a logline when the kernel module is removed.

pisound improvements:

* Added a writable sysfs object to enable scripts / user space software
to blink MIDI activity LEDs for variable duration.
* Improved hw_param constraints setting.
* Added compatibility with S16_LE sample format.
* Exposed some simple placeholder volume controls, so the card appears
in volumealsa widget.

Add missing SND_PISOUND selects dependency to SND_RAWMIDI

Without it the Pisound module fails to compile.
See https://github.com/raspberrypi/linux/issues/2366

Updates for Pisound module code:

	* Merged 'Fix a warning in DEBUG builds' (1c8b82b).
	* Updating some strings and copyright information.
	* Fix for handling high load of MIDI input and output.
	* Use dual rate oversampling ratio for 96kHz instead of single
	  rate one.

Signed-off-by: Giedrius Trainavicius <giedrius@blokas.io>
Fixing memset call in pisound.c

Signed-off-by: Giedrius Trainavicius <giedrius@blokas.io>
Fix for Pisound's MIDI Input getting blocked for a while in rare cases.

There was a possible race condition which could lead to Input's FIFO queue
to be underflown, causing high amount of processing in the worker thread for
some period of time.

Signed-off-by: Giedrius Trainavicius <giedrius@blokas.io>
Fix for Pisound kernel module in Real Time kernel configuration.

When handler of data_available interrupt is fired, queue_work ends up
getting called and it can block on a spin lock which is not allowed in
interrupt context. The fix was to run the handler from a thread context
instead.

Pisound: Remove spinlock usage around spi_sync

ASoC: pisound: use modern dai_link style

Signed-off-by: Hui Wang <hui.wang@canonical.com>
ASoC: pisound: fix the parameter for spi_device_match

Signed-off-by: Hui Wang <hui.wang@canonical.com>