ARM: stacktrace: include asm/sections.h in asm/stacktrace.h

The recent kstack erase changes appear to have uncovered an existing
issue with a missing header inclusion:

In file included from drivers/misc/lkdtm/kstack_erase.c:12:
In file included from include/linux/kstack_erase.h:16:
arch/arm/include/asm/stacktrace.h:48:21: error: call to undeclared function 'in_entry_text'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   48 |                 frame->ex_frame = in_entry_text(frame->pc);
      |                                   ^

Include asm/sections.h here so the compiler can see the in_entry_text()
declaration.

Fixes: 752ec62 ("ARM: 9234/1: stacktrace: Avoid duplicate saving of exception PC value")
Cc: Kees Cook <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Linus Walleij <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Kees Cook <[email protected]>

Author: arndb

arch/arm/include/asm/stacktrace.h

@@ -2,8 +2,9 @@
 #ifndef __ASM_STACKTRACE_H
 #define __ASM_STACKTRACE_H
 
-#include <asm/ptrace.h>
 #include <linux/llist.h>
+#include <asm/ptrace.h>
+#include <asm/sections.h>
 
 struct stackframe {
 	/*