crypto: omap-aes - Add fallback support

As setting up the DMA operations is quite costly, add software fallback
support for requests smaller than 200 bytes. This change gives some 10%
extra performance in ipsec use case.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[t-kristo@ti.com: udpated against latest upstream, to use skcipher mainly]
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>