regulator: rk808: Migrate to regulator core's simplified DT parsing code

A common simplified DT parsing code for regulators was introduced in
commit a0c7b164 ("regulator: of: Provide simplified DT parsing
method")

While at it also added RK8XX_DESC and RK8XX_DESC_SWITCH macros for the
regulator_desc struct initialization. This just makes the driver more compact.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>