soc: arm: nxp_imx: rt11xx: allow user to disable CONFIG_ADJUST_DCDC

Allow user to disable CONFIG_ADJUST_DCDC for their board, rather than
selecting it at the SOC level. The symbol still defaults to enabled,
preserving existing behavior unless a user explicitly chooses to disable
it.

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