crypto: aegis128-neon - add header for internal prototypes

gcc warns if prototypes are only visible to the caller but
not the callee:

crypto/aegis128-neon-inner.c:134:6: warning: no previous prototype for 'crypto_aegis128_init_neon' [-Wmissing-prototypes]
crypto/aegis128-neon-inner.c:164:6: warning: no previous prototype for 'crypto_aegis128_update_neon' [-Wmissing-prototypes]
crypto/aegis128-neon-inner.c:221:6: warning: no previous prototype for 'crypto_aegis128_encrypt_chunk_neon' [-Wmissing-prototypes]
crypto/aegis128-neon-inner.c:270:6: warning: no previous prototype for 'crypto_aegis128_decrypt_chunk_neon' [-Wmissing-prototypes]
crypto/aegis128-neon-inner.c:316:5: warning: no previous prototype for 'crypto_aegis128_final_neon' [-Wmissing-prototypes]

The prototypes cannot be in the regular aegis.h, as the inner neon code
cannot include normal kernel headers. Instead add a new header just for
the functions provided by this file.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>