platform/x86: acer-wmi: Add ACER_CAP_SET_FUNCTION_MODE capability flag

Not all devices supporting WMID_GUID3 support the wmid3_set_function_mode()
call, leading to errors like these:

[   60.138358] acer_wmi: Enabling RF Button failed: 0x1 - 0xff
[   60.140036] acer_wmi: Enabling Launch Manager failed: 0x1 - 0xff

Add an ACER_CAP_SET_FUNCTION_MODE capability flag, so that these calls
can be disabled through the new force_caps mechanism.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20201019185628.264473-5-hdegoede@redhat.com