kernel: migrate includes to <zephyr/...>

In order to bring consistency in-tree, migrate all kernel code to the
new prefix <zephyr/...>. Note that the conversion has been scripted,
refer to zephyrproject-rtos#45388 for more details.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
diff --git a/kernel/queue.c b/kernel/queue.c
index 42e7723..342ee89 100644
--- a/kernel/queue.c
+++ b/kernel/queue.c
@@ -11,16 +11,16 @@
  */
 
 
-#include <kernel.h>
-#include <kernel_structs.h>
+#include <zephyr/kernel.h>
+#include <zephyr/kernel_structs.h>
 
-#include <toolchain.h>
-#include <wait_q.h>
+#include <zephyr/toolchain.h>
+#include <zephyr/wait_q.h>
 #include <ksched.h>
-#include <init.h>
-#include <syscall_handler.h>
+#include <zephyr/init.h>
+#include <zephyr/syscall_handler.h>
 #include <kernel_internal.h>
-#include <sys/check.h>
+#include <zephyr/sys/check.h>
 
 struct alloc_node {
 	sys_sfnode_t node;