Combine config.txt for 32-bit and 64-bit models

Use 64-bit for RPi 3, 4, 400 and Zero 2, and 32-bit for all other models
No more renaming of config.txt by the user required
https://github.com/probonopd/MiniDexed/issues/23#issuecomment-1047481397
Thanks @rsta2

src/config.txt

@@ -0,0 +1,23 @@
+#
+# Use 64-bit for RPi 3, 4, 400 and Zero 2, and 32-bit for all other models
+#
+
+[pi02]
+arm_64bit=1
+kernel=kernel8.img
+
+[pi3]
+arm_64bit=1
+kernel=kernel8.img
+
+[pi3+]
+arm_64bit=1
+kernel=kernel8.img
+
+[pi4]
+arm_64bit=1
+armstub=armstub8-rpi4.bin
+kernel=kernel8-rpi4.img
+
+[all]
+sounddev=sndpwm