kernel: thread: fix thread priority off-by-one error

Setting CONFIG_NUM_PREEMPT_PRIORITIES to 128 causes the idle thread to be
assigned priority 128, which exceeds the int8_t range. This results in the
idle thread being assigned the highest priority (-128) instead of the
lowest, causing threads to not wake up from k_sleep.

Restrict the range of CONFIG_NUM_PREEMPT_PRIORITIES to 0 to 127 to ensure
the idle thread always has the lowest priority.

Signed-off-by: Jonas Spinner <jonas.spinner@burkert.com>

Author: jonas-5ae29c

kernel/Kconfig

@@ -53,7 +53,7 @@ config NUM_PREEMPT_PRIORITIES
 	int "Number of preemptible priorities" if MULTITHREADING
 	default 0 if !MULTITHREADING
 	default 15
-	range 0 128
+	range 0 127
 	help
 	  Number of preemptible priorities available in the system. Gives access
 	  to priorities 0 to CONFIG_NUM_PREEMPT_PRIORITIES - 1.