qed: Report error for unsupported features

Instead of just returning -ENOTSUP, generate a more detailed error.

Unfortunately we don't have a helpful text for features that we don't know yet,
so just print the feature mask. It might be useful at least if someone asks for
help.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Acked-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
(cherry picked from commit 10b758e8)