x86/xen: Fix xen head ELF annotations

Mark the ends of the startup_xen and hypercall_page code sections.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/3a80a394d30af43d9cefa1a29628c45ed8420c97.1505764066.git.jpoimboe@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>