pcnet-pci: mark I/O and MMIO as LITTLE_ENDIAN

Now that the memory subsystem is propagating the endianness correctly,
the pcnet-pci device should have its I/O ports and MMIO memory marked
as LITTLE_ENDIAN, as PCI devices are little endian.

This makes the pcnet-pci NIC to work again on big endian MIPS Malta
(default NIC).

Cc: qemu-stable@nongnu.org
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>