hwrng: amd - manage resource allocation

As amd driver doesn't bind to PCI device, we'd better manage reource
allocation on our own to disallow (possible) conflicts.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>