usb: chipidea: imx: do not use preprocessor conditionals for PM

Use preprocessor conditionals for CONFIG_PM and CONFIG_PM_SLEEP is
not necessary since SET_SYSTEM_SLEEP_PM_OPS and SET_RUNTIME_PM_OPS does
that internally.

It is also the preferred way according to our coding style guidelines.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>