crypto: gf128mul - rename the byte overflow tables

Though the GF(2^128) byte overflow tables were named the "lle" and "bbe"
tables, they are not actually tied to these element formats
specifically, but rather to particular a "bit endianness".  For example,
the bbe table is actually used for both bbe and ble multiplication.
Therefore, rename the tables to "le" and "be" and update the comment to
explain this.

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