crypto: aegis128 - Move simd prototypes into aegis.h

This patch fixes missing prototype warnings in crypto/aegis128-neon.c.

Fixes: a4397635

 ("crypto: aegis128 - provide a SIMD...")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>