soc: nxp: imxrt: Remove ifdef around DCDC

The DCDC should be on all the platforms and the functions and structs
should therefore be defined on all the platforms. So the ifdef is not
needed, we can remove it to increase code compilation coverage unity
across configurations slightly. Compiler should optimize out the block
when IS_ENABLED is false statically.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>