x86/mm: Re-enable DEBUG_TLBFLUSH for X86_32

CONFIG_INVLPG got removed in commit
094ab1db ("x86, 386 removal:
Remove CONFIG_INVLPG").

That commit left one instance of CONFIG_INVLPG untouched, effectively
disabling DEBUG_TLBFLUSH for X86_32. Since all currently supported
x86 CPUs should now be able to support that option, just drop the entire
sub-dependency.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Link: http://lkml.kernel.org/r/1363262077.1335.71.camel@x61.thuisdomein


Signed-off-by: Ingo Molnar <mingo@kernel.org>