linker: move all linker headers to include/linker

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/kernel/stack.c b/kernel/stack.c
index b5d59d6..01dd4c1 100644
--- a/kernel/stack.c
+++ b/kernel/stack.c
@@ -12,7 +12,7 @@
 #include <kernel_structs.h>
 #include <debug/object_tracing_common.h>
 #include <toolchain.h>
-#include <sections.h>
+#include <linker/sections.h>
 #include <ksched.h>
 #include <wait_q.h>
 #include <misc/__assert.h>