crypto: omap-aes - Add support for cases of unaligned lengths

For cases where offset/length of on any page of the input SG is not aligned by
AES_BLOCK_SIZE, we copy all the pages from the input SG list into a contiguous
buffer and prepare a single element SG list for this buffer with length as the
total bytes to crypt.

This is requried for cases such as when an SG list of 16 bytes total size
contains 16 pages each containing 1 byte. DMA using the direct buffers of such
instances is not possible.

For this purpose, we first detect if the unaligned case and accordingly
allocate enough number of pages to satisfy the request and prepare SG lists.
We then copy data into the buffer, and copy data out of it on completion.

Signed-off-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>