regulator: core: Mark all DT based boards as having full constraints

Since DT doesn't provide an idiomatic mechanism for enabling full
constraints and since it's much more natural with DT to provide them
just assume that a DT enabled system has full constraints.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>