The introduction of cc2c05a90c caused
CONFIG_MCUX_LPTMR_TIMER to always be enabled for boards where the NXP LPTMR
is enabled in the board devicetree.
Using this low-power timer as system timer only makes sense when using
power management. Otherwise, it just results in a lower tick resolution and
non-tickless operation.
Add dependency on CONFIG_PM for CONFIG_MCUX_LPTMR_TIMER.
Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>