x86: fix up some bad global variable names in mm/init.c

Impact: cleanup

The table_start, table_end, and table_top are too generic for global
namespace so rename them to be more specific.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1236257708-27269-15-git-send-email-penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>