toshiba_acpi: Support alternate hotkey interfaces

There are two types of problems that prevent hotkeys from working
on many of the machines supported by toshiba_acpi. The first of
these is the lack of a functioning SCI for hotkey events. For these
machines it is possible to filter the Fn keypresses from the
keyboard and generate a notification by executing the ACPI NTFY
method.

The second problem is a lack of support for HCI_SYSTEM_EVENT, which
is used for reading the hotkey scancodes. On these machines the
scancodes can be read by executing the ACPI NTFY method.

This patch fixes both problems by installing an i8042 filter when
the NTFY method is present to generate notifications and by
detecting which of INFO or HCI_SYSTEM_EVENT is supported for
reading scancodes. If neither method of reading scancodes is
supported, the hotkey input device is not registered.

Signed-off-by: Azael Avalos <coproscefalo@gmail.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>