Backport some DRBG renamings and typo fixes

In commit 8bf36651 some renamings andd typo fixes were made
while adding back the DRBG-HMAC and DRBG-HASH implementation.
Since the commit could not be backported, a lot of unnecessary
differences between master and 1.1.1 were introduced.

These differences result in tiresome merge conflicts when
cherry-picking. To minimize these merge-conflicts, this patch
ports all 'non-feature' changes of commit 8bf36651
(e.g., renamings of private variables, fixes of typographical
errors, comment changes) manually back to 1.1.1.

The commits a83dc59a (#7399) and 8817215d

 (#7456)
failed to cherry-pick previously to 1.1.1, with this patch
they both cherry-pick without conflicts.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/7505)