Move rtems cfg-ed import with the others

[tgross35]

Clean up code added in #3866

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[tgross35]

@thesummer just noticed this when starting a backport, is there any reason it was in a separate cfg block in #3866?

[thesummer]

@thesummer just noticed this when starting a backport, is there any reason it was in a separate cfg block in #3866?

@tgross35 Yes, IIRC it is because I also need the arm config block enabled. If it is in the general else-if chain it will be only one of the two.
Atm one could include the arm module also in the rtems branch. However, this might need to be changed if other RTEMS targets are added (but we can also change it when the time comes).