crypto: lrw - prefix function and struct names with "lrw"

Overly-generic names can cause problems like naming collisions,
confusing crash reports, and reduced grep-ability.  E.g. see
commit d099ea6e ("crypto - Avoid free() namespace collision").

Clean this up for the lrw template by prefixing the names with "lrw_".

(I didn't use "crypto_lrw_" instead because that seems overkill.)

Also constify the tfm context in a couple places.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>