Don't call EVP_CIPHER_CTX_block_size() to find the block size

Don't call EVP_CIPHER_CTX_block_size() to find the block size

The EVP lib was calling EVP_CIPHER_CTX_block_size(), which in turn calls
EVP_CIPHER_block_size() in order to find the block_size in every
EVP_EncryptUpdate() call. This adds a surprising amount of overhead when
using speed to test aes-128-cbc. Since we're in the EVP lib itself, we can
just directly access this value.

To test performance I ran the command:
openssl speed -evp aes-128-cbc -bytes 16 -seconds 30

For the before and after, I ran this twice and discarded the first result
to "warm up" my machine.

Before:
aes-128-cbc     716949.71k

After:
aes-128-cbc     742807.11k

This represents a performance improvement of about 4%

Partially fixes #13407

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/13734)