x86/um: Annotate data appropriately

Use the new SYM_DATA_START and SYM_DATA_END_LABEL macros for vdso_start.

Result is:
  0000  2376 OBJECT  GLOBAL DEFAULT    4 vdso_start
  0948     0 OBJECT  GLOBAL DEFAULT    4 vdso_end

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: linux-arch@vger.kernel.org
Cc: linux-um@lists.infradead.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: user-mode-linux-devel@lists.sourceforge.net
Cc: user-mode-linux-user@lists.sourceforge.net
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20191011115108.12392-14-jslaby@suse.cz