partrt: Replaced partrt_cpumask.c with partrt_bitmap.c

Bitmap handling has been generalized to be able to handle other cases than just
CPUs. This means that nr_cpus() function need to be used when creating a new
bitmap to force a static size for the bitmap, so that complement functions
work as intended.

Signed-off-by: Mats Liljegren <mats.liljegren@enea.com>