platform/x86: thinkpad_acpi: guard generic hotkey case

Currently when dispatching hotkeys we check if the scancode is in
the range of 0 and TPACPI_HOTKEY_MAP_LEN, although the bottom 20
entries in the hotkey keymap are already adaptive keycodes.
Therefore we introduce a TP_ACPI_HOTKEYSCAN_ADAPTIVE_START and
ensure that we are in the range 0 and ADAPTIVE_START for the generic
keycode case.

Signed-off-by: Christian Kellner <ckellner@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>