Revert "x86, extable: Disable presorted exception table for now"

sortextable now works with relative entries, re-enable it.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Link: http://lkml.kernel.org/r/1335291795-26693-3-git-send-email-ddaney.cavm@gmail.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>