xen/pci: Get rid of verbose_request and use dev_dbg() instead

Information printed under verbose_request is clearly used for debugging
only. Remove it and use dev_dbg() instead.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/1590719092-8578-1-git-send-email-boris.ostrovsky@oracle.com
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>