ALSA: scarlett2: Add device_setup option to use FCP driver

Add a new device_setup option (SCARLETT2_USE_FCP_DRIVER = 0x08) that
allows users to opt in to using the new FCP driver instead of the
existing scarlett2 driver for their device. This provides a way to
test the new FCP driver on existing supported hardware while keeping
the Scarlett2 driver as the default.

When the SCARLETT2_USE_FCP_DRIVER bit is set in device_setup, the
scarlett2 driver initialisation will hand off to the FCP driver
instead of proceeding with its own initialisation. The FCP driver then
provides access to the device via its hwdep interface.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>

ALSA: scarlett2: Increase mixer range to +12dB

The values loaded into the mixer are 16-bit values, with 8192
representing 0dB, going up to a current maximum of 16345 (+6dB). All
supported interfaces have no problem going up to 32612 (+12dB), so
update SCARLETT2_MIXER_MAX_DB and scarlett2_mixer_values[] to allow
for this.

Tested with:
- Scarlett 2nd Gen 6i6, 18i8, 18i20
- Scarlett 3rd Gen 4i4, 8i6, 18i8, 18i20
- Scarlett 4th Gen Solo, 2i2, 4i4
- Clarett+ 2Pre, 4Pre, 8Pre
- Vocaster One and Two

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>

ALSA: scarlett2: Add S/PDIF source selection controls

Add S/PDIF Source/Digital I/O Mode selection controls for the Scarlett
3rd Gen 18i8/18i20 and Clarett 4Pre/8Pre interfaces. These models have
both coax S/PDIF and optical inputs, and the optical inputs are
switchable between being used as S/PDIF and ADAT inputs. The Scarlett
3rd Gen 18i20 also has a "Dual ADAT" mode for 8-channel audio at
88.2/96kHz.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>

ALSA: scarlett2: Add S/PDIF source selection controls

Add S/PDIF Source/Digital I/O Mode selection controls for the Scarlett
3rd Gen 18i8/18i20 and Clarett 4Pre/8Pre interfaces. These models have
both coax S/PDIF and optical inputs, and the optical inputs are
switchable between being used as S/PDIF and ADAT inputs. The Scarlett
3rd Gen 18i20 also has a "Dual ADAT" mode for 8-channel audio at
88.2/96kHz.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>

ALSA: scarlett2: Add Bluetooth volume control for Vocaster Two

The Vocaster Two has a Bluetooth module with a volume control. Add a
corresponding ALSA mixer control.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>

ALSA: scarlett2: Add PCM Input Switch for Solo Gen 4

When the Direct button on the Solo Gen 4 is held for 3 seconds, the
PCM 1 and 2 inputs are toggled between DSP Outputs 1 and 2, and Mixer
Outputs E and F. This patch adds the corresponding ALSA control.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>

ALSA: scarlett2: Add PCM Input Switch for Solo Gen 4

When the Direct button on the Solo Gen 4 is held for 3 seconds, the
PCM 1 and 2 inputs are toggled between DSP Outputs 1 and 2, and Mixer
Outputs E and F. This patch adds the corresponding ALSA control.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>

ALSA: scarlett2: Add mux notification callback for Solo Gen 4

When the Direct button the Solo Gen 4 is held for 3 seconds, the PCM 1
and 2 inputs are toggled between DSP Outputs 1 and 2, and Mixer
Outputs E and F. This patch adds a notification callback to re-read
the mux controls when that happens.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>

ALSA: scarlett2: Add missing check with firmware version control

scarlett2_add_firmware_version_ctl() may return an error, but the
return value was not being checked. Add the missing check.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>