Switch to a voluntary kernel preemption.

The respeaker mic hats and possibly (many) others are using the
x-powers ac108 adc chip however the driver of this chip is not
compatible with 64bit PREEMPT kernels crashing the drivers with
"BUG: scheduling while atomic" spinlock issues.

PREEMPT is used for low latency desktops
PREEMPT_NONE is used for servers

As we are not a (low-latency needed) desktop however not a server
as well, the middle ground actually works perfectly fine with
the benefit of having a more stable respeaker driver.

This accounts for ALL different respeaker HATs except the 2-mic
as that one is based on the WM8960 chip which is actually already
supported mainline if you want anyway.

buildroot-external/board/raspberrypi/kernel.config

@@ -4,5 +4,8 @@ CONFIG_SND_SOC_TAS5086=m
 # CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE is not set
 CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
 
+CONFIG_PREEMPT_VOLUNTARY=y
+# CONFIG_PREEMPT is not set
+
 CONFIG_ZRAM=y
 CONFIG_ZSMALLOC=y