platform/x86: thinkpad_acpi: silence false-positive-prone pr_warn

Do not consider unknown HKEY events in the 0x6000 range to be thermal
warnings.  Instead, handle them as a generic unknown HKEY event, which
are reported to the kernel log at priority "notice", and do not trigger
a thermal registers state dump to the log.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Tested-by: Jordan Glover <Golden_Miller83@protonmail.ch>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>