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).

include/config/libinput.h

@@ -38,6 +38,7 @@ struct libinput_category {
 };
 
 enum lab_libinput_device_type get_device_type(const char *s);
+const char *libinput_device_type_name(enum lab_libinput_device_type type);
 struct libinput_category *libinput_category_create(void);
 struct libinput_category *libinput_category_get_default(void);