[BUGFIX] Placeholder attribute without useOrOverridePlaceholder

The placeholder configuration for a TCA field will now be considered
independently from the "mode" being set to "useOrOverridePlaceholder".
If a placeholder is set in the TCA it will be rendered. The mode
setting only changes the behavior of the NULL checkbox.

Resolves: #59129
Releases: master, 6.2
Change-Id: Ice7681d644623a5e94cbdd22743ddf5aab8919a9
Reviewed-on: http://review.typo3.org/35175
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>