regulator: max77693: Let core parse DT and drop board files support

Simplify the driver by removing board file support and letting
regulator core to parse DT.

The max77693 regulator driver is used only on Exynos based boards which
are DT-only. Board files for Exynos are not supported.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>