package/botan: update supported architectures

package/botan: update supported architectures

- aarch64, powerpc64le and s390x are supported since version 2.5.0 and
  https://github.com/randombit/botan/commit/5f55f0eac95cd6f1c2962aef261af285bf37bfb6
- sparc64 is supported since version 2.5.0 and
  https://github.com/randombit/botan/commit/7e6aea7a9bff0714756aff5c7470c5c55cb31e0c
- riscv is supported since version 2.8.0 and
  https://github.com/randombit/botan/commit/b9aafd67002be96bf00eea4e7791804693ba4b1f

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>