ALSA: usb-audio: Add support for Presonus Studio 1810c

This patch adds support for Presonus Studio 1810c, a usb interface
that's UAC2 compliant with a few quirks and a few extra hw-specific
controls. I've tested all 3 altsettings and the added switch
controls and they work as expected.

More infos on the card:
https://www.presonus.com/products/Studio-1810c

Note that this work is based on packet inspection with
usbmon. I just wanted to get this card to work for using
it on our open-source radio station:
https://github.com/UoC-Radio

v2 address issues reported by Takashi:
* Properly get/set enum type controls
* Prevent race condition on switch_get/set
* Various control naming changes
* Various coding style fixes

v3 improve readability of sample rate filtering
and some other minor changes.

Signed-off-by: Nick Kossifidis <mickflemm@gmail.com>
Link: https://lore.kernel.org/r/5e47481a.1c69fb81.befb3.8dac@mx.google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/Makefile b/sound/usb/Makefile
index 78edd7d..5603102 100644
--- a/sound/usb/Makefile
+++ b/sound/usb/Makefile
@@ -13,6 +13,7 @@
 			mixer_scarlett.o \
 			mixer_scarlett_gen2.o \
 			mixer_us16x08.o \
+			mixer_s1810c.o \
 			pcm.o \
 			power.o \
 			proc.o \