xen/pcifront: Remove usage of struct timeval

struct timeval uses a 32-bit field for representing seconds, which
will overflow in the year 2038 and beyond. Replace struct timeval with
64-bit ktime_t which is 2038 safe.  This is part of a larger effort to
remove instances of 32-bit timekeeping variables (timeval, time_t and
timespec) from the kernel.

Signed-off-by: Tina Ruchandani <ruchandani.tina@gmail.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>