Add option to disable Optimus DSM (GH-14)

Necessary for one (some?) older laptops like the Lenovo T410s. Usage: put
"options bbswitch skip_optimus_dsm=1" in your modprobe.conf
Linux 3.8 compatibility hack

Since the following commit, the device would not turn off because the power
state is unknown. Until a fix is released in Linux (or until I know what
better to do), I just assume the power state D0.

commit ddc150f7a33ae0c9cb16eaac3641abc00f56316f
Author: Lv Zheng <lv.zheng@intel.com>
Date:   Fri Nov 16 02:46:28 2012 +0100

    ACPI / PM: Add check preventing transitioning to non-D0 state from D3.

    No power transitioning from D3 state up to a non-D0 state is allowed
    so make acpi_device_set_power() fail and complain if such a transition
    is attempted.

    Signed-off-by: Lv Zheng <lv.zheng@intel.com>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>