[BUGFIX] Native DateTime values cannot be mapped from storage

DateTime values that are stored with an accordant (native) type
cannot be mapped correctly since a unix timestamp is expected.
The TCA configuration property 'dbType' for 'date' and
'datetime' fields reflects the non-timestamp way.

Change-Id: I214c857bcb8b0380554b481870ab5f3556713226
Fixes: #46193
Releases: 6.0, 6.1
Reviewed-on: https://review.typo3.org/19009
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring