arch: arm: cortex_m: Rework DT_NUM_IRQ_PRIO_BITS

To remove the need to have DT_NUM_IRQ_PRIO_BITS defined in every
dts_fixup.h we can just handle the few variant cases in irq.h.  This
allows us to remove DT_NUM_MPU_REGIONS from all the dts_fixup.h files.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
7 files changed