USB: add check to detect host controller hardware removal

This patch (as1391) fixes a problem that can occur when USB host
controller hardware is hot-unplugged.  If no interrupts are generated
by the unplug then the HCD may not realize that the controller is
gone, and the subsequent unbind may hang waiting for interrupts that
never arrive.

The solution (for PCI-based controllers) is to call the HCD's
interrupt handler at the start of usb_hcd_pci_remove().  If the
hardware is gone, the handler will realize this when it tries to read
the controller's status register.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>