platform/x86: asus-wmi: Switch fan boost mode

The WMI exposes a write-only device ID where up to three fan modes can be
switched on some laptops (TUF Gaming FX505GM). There is a hotkey
combination Fn-F5 that does have a fan icon, which is designed to toggle
between fan modes. The DSTS of the device ID returns information about the
presence of this capability and the presence of each of the two additional
fan modes as a bitmask (0x01 - overboost present, 0x02 - silent present)
[1].

Add a SysFS entry that reads the last written value and updates value in
WMI on write and a hotkey handler that toggles the modes taking into
account their availability according to DSTS.

Modes:
* 0x00 - normal or balanced,
* 0x01 - overboost, increased fan RPM,
* 0x02 - silent, decreased fan RPM

[1] Link: https://lkml.org/lkml/2019/4/12/110

Signed-off-by: Yurii Pavlovskyi <yurii.pavlovskyi@gmail.com>
Suggested-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>