[PATCH] airo: Make /sys/bus/pci/drivers/airo/{,un}bind work

The way airo.c keeps track of all its devices is complicated and buggy
as well (del_airo_dev forgets to free the memory add_airo_dev allocates).
It's cleaner to use the standard list primitives.
While we're at it, it's not necessary to put PCI cards in the list, because
the kernel already keeps track of them. We can take advantage of it and
use the .remove callback as it was meant to be.
This makes /sys/bus/pci/drivers/airo/{,un}bind work.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>