Xen i386 xen-head.S fix sections mixup

Xen i386 xen-head.S fix sections mixup

xen-head.S does not come back to the data section, leaving the text section
as current section. It causes problems with a slightly enhanced DEBUG_RODATA
that supports CONFIG_HOTPLUG and bringing a CPU up after the text has been
marked read-only: reference to early_gdt_descr causes a page fault.

Updates:

- It should be using pushsection/popsection.
- Actually, the push/popsections around the ELFNOTEs are redundant; ELFNOTE()
  does its own push/popsection to put things into the appropriate .note* section
  anyway.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>