drivers: regulator: pca9420: fix support for DVS modes

Fix support for DVS modes, as the dvs_state_set implementation
previously had the mask and value parameters in the
i2c_reg_update_byte_dt function swapped.

Also, record the active DVS state and update the voltage get/set and
regulator enable/disable function to target the active DVS mode. This
will enable a user to configure multiple run modes, and modify target
voltages for those modes when in the new mode. When a user is utilizing
the MODESEL pins, update the active state but return an error so that
the application can still edit settings for the new DVS mode once it has
reconfigured the appropriate pins.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>