seat: improve debug logging when configuring input devices

I needed to debug an input configuration issue and found the debug
output not-super-helpful, so I made some improvements:

- Print the name and "sysname" (e.g. event11) of the device being
  configured. Note that the name alone isn't enough since there can
  be multiple identically-named devices.

- Print the config category matched for each device.

- Print the config values (if any) being applied. For enums, only the
  numeric value is printed since I'm lazy.

- Don't print "pointer acceleration configured" if neither a pointer
  speed nor acceleration profile is configured (it's confusing).

src/config/libinput.c

@@ -51,6 +51,25 @@ get_device_type(const char *s)
 	return LAB_LIBINPUT_DEVICE_NONE;
 }
 
+const char *
+libinput_device_type_name(enum lab_libinput_device_type type)
+{
+	switch (type) {
+	case LAB_LIBINPUT_DEVICE_NONE:
+		break;
+	case LAB_LIBINPUT_DEVICE_DEFAULT:
+		return "default";
+	case LAB_LIBINPUT_DEVICE_TOUCH:
+		return "touch";
+	case LAB_LIBINPUT_DEVICE_TOUCHPAD:
+		return "touchpad";
+	case LAB_LIBINPUT_DEVICE_NON_TOUCH:
+		return "non-touch";
+	}
+	/* none/invalid */
+	return "(none)";
+}
+
 struct libinput_category *
 libinput_category_create(void)
 {