sam3x: report correct number of IRQ priority bits
sam3x: report correct number of IRQ priority bits

The Sam3x HAL defines __NVIC_PRIO_BITS to 4.
Fixes an issue where interrupt priorities and masking
were not being done correctly.

Issue: ZEP-2243
Signed-off-by: Andrew Boie <aab045b28152628be6af0e556050d0381fd0a34d@intel.com>

bigdinotech/zephyr,bigdinotech/zephyr,bigdinotech/zephyr,bigdinotech/zephyr,bigdinotech/zephyr