crypto: mediatek - move to generic async completion

The mediatek driver starts several async crypto ops and waits for their
completions. Move it over to generic code doing the same.

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Acked-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>