virtio: change memcpy to guest reads

virtio: change memcpy to guest reads

When accessing the device specific virtio config space, we memcpy
the data into a variable in QEMU. At that point we're basically
pulling host endianness into the game which is a really bad idea.

So instead, let's use the target specific load/store helpers for
memory pointers which fetch things in target endianness. The whole
array is already populated in target endianness anyways
(see virtio-blk).

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>