[BUGFIX] FAL storage repo uses hard-coded enableFields

[BUGFIX] FAL storage repo uses hard-coded enableFields

The storage repository has hardcoded SQL where clauses
for deleted and hidden.
Solution: Create a new function that returns the additional
where clause, based on the frontend / backend context.

Change-Id: I6258ee639d4cc8d97a9712596baeb86ea1e576b6
Resolves: #41715
Releases: 6.0
Reviewed-on: http://review.typo3.org/15445
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter