zephyr: use k_thread_entry_t everywhere

In various places, a private _thread_entry_t, or the full prototype
were being used. Be consistent and use the same typedef everywhere.

Signen-off-by: Andrew Boie <andrew.p.boie@intel.com>
diff --git a/kernel/include/nano_internal.h b/kernel/include/nano_internal.h
index 051ffe4..2832645 100644
--- a/kernel/include/nano_internal.h
+++ b/kernel/include/nano_internal.h
@@ -40,12 +40,11 @@
 #endif
 FUNC_NORETURN void _Cstart(void);
 
-extern FUNC_NORETURN void _thread_entry(void (*)(void *, void *, void *),
-			  void *, void *, void *);
+extern FUNC_NORETURN void _thread_entry(k_thread_entry_t entry,
+			  void *p1, void *p2, void *p3);
 
 extern void _new_thread(struct k_thread *thread, k_thread_stack_t pStack,
-			size_t stackSize,
-			void (*pEntry)(void *, void *, void *),
+			size_t stackSize, k_thread_entry_t entry,
 			void *p1, void *p2, void *p3,
 			int prio, unsigned int options);