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

In order to bring consistency in-tree, migrate all subsystems 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/subsys/tracing/tracing_backend_ram.c b/subsys/tracing/tracing_backend_ram.c
index 149402e..2f82197 100644
--- a/subsys/tracing/tracing_backend_ram.c
+++ b/subsys/tracing/tracing_backend_ram.c
@@ -5,7 +5,7 @@
  */
 
 #include <ctype.h>
-#include <kernel.h>
+#include <zephyr/kernel.h>
 #include <string.h>
 #include <tracing_core.h>
 #include <tracing_buffer.h>