crypto: aead - Add support for on-stack AEAD req allocation

crypto: aead - Add support for on-stack AEAD req allocation

This patch introduces infrastructure for allocating req objects on the
stack for AEADs. The additions mirror the existing sync skcipher APIs.
This can be used in cases where simple sync AEAD operations are being
done. So allocating the request on stack avoides possible out-of-memory
errors.

The struct crypto_sync_aead is a wrapper around crypto_aead and should
be used in its place when sync only requests will be done on the stack.
Correspondingly, the request should be allocated with
SYNC_AEAD_REQUEST_ON_STACK().

Similar to sync_skcipher APIs, the new sync_aead APIs are wrappers
around the regular aead APIs to facilitate sync only operations. The
following crypto APIs are added:
 - struct crypto_sync_aead
 - crypto_alloc_sync_aead()
 - crypto_free_sync_aead()
 - crypto_aync_aead_tfm()
 - crypto_sync_aead_setkey()
 - crypto_sync_aead_setauthsize()
 - crypto_sync_aead_authsize()
 - crypto_sync_aead_maxauthsize()
 - crypto_sync_aead_ivsize()
 - crypto_sync_aead_blocksize()
 - crypto_sync_aead_get_flags()
 - crypto_sync_aead_set_flags()
 - crypto_sync_aead_clear_flags()
 - crypto_sync_aead_reqtfm()
 - aead_request_set_sync_tfm()
 - SYNC_AEAD_REQUEST_ON_STACK()

Signed-off-by: T Pratham <t-pratham@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>