linux-wandboard

thinkpad-acpi: update HKEY and hotkey subdriver documentation (v2)

Update the hotkey driver documentation to match the behaviour
of the fixed NVRAM polling code.

This also documents some HKEY events such as the alarms,
which is very important information.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>