[PATCH] ASoC: rt715:add Mic Mute LED control support

[Pierre-Louis Bossart]

> I don't think it came through in the commit message, but I wanted to mention
> in the system that prompted this software does not control the LED.  The LED
> is actually controlled by hardware, but has circuitry to delay the hardware
> mute until software mute is complete to avoid any "popping noises".
> 
> This patch along with the platform/x86 patch:
> https://patchwork.kernel.org/project/platform-driver-x86/patch/20201103125542.8572-1-Perry_Yuan@Dell.com/
> complete that loop.
> 
> The flow is:
> User presses mute key, dell-wmi receives event, passes to dell-privacy-wmi.
> This emits to userspace as KEY_MICMUTE.  Userspace processes it and via UCM
> switches get toggled.  The codec driver (or subsystem perhaps) will use LED
> trigger to notify to change LED.  This gets picked up by dell-privacy-acpi.
> 
> dell-privacy-acpi doesn't actually change LED, but notifies that SW mute was
> done.
> 
> If none of that flow was used the LED and mute function still work, but there
> might be the popping noise.

Side note that the existing UCM config for RT715 does not do what I 
suggested, it seems we are using an incorrect configuration for 
CaptureSwitch and CaptureVolume:

CaptureSwitch "PGA5.0 5 Master Capture Switch"
	      CaptureVolume "PGA5.0 5 Master Capture Volume"		 
CaptureVolume "PGA5.0 5 Master Capture Volume"

That should be an RT715 control, not an SOF one. This was brought to our 
attention this morning. Probably a copy-paste from the DMIC case, likely 
needs to be changed for both RT715 and RT715-sdca cases.

https://github.com/thesofproject/linux/issues/2544#issuecomment-721231103