[BUGFIX] Sorting not respected for backend layout dropdowns

The core record backend_layout can be sorted manually, but this is not
reflected in the pages TCA for the dropdowns backend_layout and
backend_layout_next_level.

This patch fixes this issue by adding the sorting in the foreign_where
clause

Thanks to Frans Saris for reporting this issue

Change-Id: I04680278075ddc0de69600423be5fe783e34f562
Resolves: #47688
Releases: 4.7, 6.0, 6.1, 6.2
Reviewed-on: https://review.typo3.org/20444
Reviewed-by: Wouter Wolters
Reviewed-by: Steffen Müller
Tested-by: Steffen Müller
Reviewed-by: Frans Saris
Tested-by: Frans Saris
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring