platform/x86: acer-wmi: Add new force_caps module parameter

Add a new force_caps module parameter to allow overriding the drivers
builtin capability detection mechanism.

This can be used to for example:
-Disable rfkill functionality on devices where there is an AA OEM DMI
 record advertising non functional rfkill switches
-Force loading of the driver on devices with a missing AA OEM DMI record

Note that force_caps is -1 when unset, this allows forcing the
capability field to 0, which results in acer-wmi only providing WMI
hotkey handling while disabling all other (led, rfkill, backlight)
functionality.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20201019185628.264473-4-hdegoede@redhat.com