x86/mm: Avoid superflous leave_mm() in the TLB flush path

x86/mm: Avoid superflous leave_mm() in the TLB flush path

If just one page VA tlb is required to be flushed and current
task is in lazy TLB state, doing leave_mm() is superfluous
because it flushes the whole TLB.  This can reduce some TLB
miss.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>