x86, vmlinux.lds: fix relocatable symbols

__init_begin/_end symbols should be inside sections as well,
otherwise the relocatable kernel gets confused when freeing
init sections in the wrong place.

[ Impact: fix bootup crash ]

Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Tim Abbott <tabbott@MIT.EDU>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20090429105056.GA28720@uranus.ravnborg.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>