crypto: s5p-sss - Constify pointed data (arguments and local variables)

Improve the code (safety and readability) by indicating that data passed
through pointer is not modified.  This adds const keyword in many places,
most notably:
 - the driver data (pointer to struct samsung_aes_variant),
 - scatterlist addresses written as value to device registers,
 - key and IV arrays.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>