staging: virtpci: Remove no-op suspend/resume functions

The virtpci bus driver still uses the legacy suspend/resume callbacks. In
their current implementation these callbacks only contain a macro that
always expands to 'do { } while(0)'. So instead of converting them to dev PM
ops just remove them.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>