[trusty] dell-laptop: Only install the i8042 filter when rfkill is active

[Yidi Lin]

BugLink: https://bugs.launchpad.net/bugs/1289238

Bug report only mentions linux-lts-saucy. But this bug also affects
trusty kernel.
For saucy kernel, the bug is fixed by "ACPI: blacklist win8 OSI for
Dell Inspiron 7737".

For trusty kernel, this patch should also be applied.
The rfkill functionality is only enabled on some specific models after
Linux 3.13-rc2.
This patch avoids troublesome rfkill query when hotkey gets pressed on
non whitelisted laptops.

commit 97f440c23f2b02fac8af0558cba9ca0bed603794
Author: Hans de Goede <hdegoede at redhat.com>
Date:   Tue Dec 24 20:34:01 2013 +0100

    dell-laptop: Only install the i8042 filter when rfkill is active

    Installing the i8042 filter is not useful on machines where rfkill is not
    whitelisted, so move the filter installation into dell_setup_rfkill,
    after the whitelist check.

    This avoids doing a needless and potentially troublesome rfkill query
    (dell_send_request(buf, 17, 11)) when the wireless Fn key gets pressed on
    non whitelisted laptops.

    This patch was written as a result of:
    https://bugzilla.redhat.com/show_bug.cgi?id=1045807
    It is not yet clear if this is related, but it is a good idea to
not register
    the i8042 filter in general.

    Signed-off-by: Hans de Goede <hdegoede at redhat.com>
    Signed-off-by: Matthew Garrett <matthew.garrett at nebula.com>