crypto: mediatek - regroup functions by usage

This patch only regroup functions by usage.
This will help to integrate the GCM support patch later by
adjusting some shared code section, such as common code which
will be reused by GCM, AES mode setting, and DMA transfer.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>