drm/exynos: remove ifdeferry from initialization code

The patch replaces separate calls to driver (de)registration by
loops over the array of drivers. As a result it significantly
decreases number of ifdefs. Additionally it moves device registration
related ifdefs to header file.

Changelog v2:
- Rebased.
- Consider non kms driver in respect to infinite loop issue.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>