cmake: LD: Allow input sections to remain unsorted

We have users that have problems in their linker scripts where the
order of input sections matters.

To allow users to use the latest Zephyr while working on a fix to
their linker scripts we add an option to allow leaving the sections
unsorted.

See discussion here for more details
https://github.com/zephyrproject-rtos/zephyr/pull/14183



Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>