Fix forcedeth hibernate/wake-on-lan problems

This patch is the minimal amount of code needed to support
wake-on-lan in platform mode properly (i.e. "ethtool -s eth0 wol g"
is sufficient, no additional magic needed) for me.

This is derived from David Brownells patch
(http://lists.laptop.org/pipermail/devel/2007-April/004691.html).
However I decided to move the hook into pci-acpi.c since the other
two pci hooks also live there and pci and acpi are the only users of
the platform_enable_wakeup-hook.

As a 'side-effect' this also makes wake on usb activity work for me
and I had to disable usb wakeup (which is enabled by default) using
the power/wakeup sysfs functionality ("echo disabled >
${sysfs_path_to_device}/power/wakeup").

(BTW I first thought the 'immediate reboot because of usb wake' effect is
caused by the optical mouse generating a wake event, but it rather
seems to be a problem with a flaky secondary usb host controller,
which sees a connected device where nothing is attached)

Signed-off-by: Tobias Diedrich <ranma+kernel@tdiedrich.de>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>