x86/mm/cpa: Move flush_tlb_all()

There is an atom errata, where we do a local TLB invalidate right
before we return and then do a global TLB invalidate.

Move the global invalidate up a little bit and avoid the local
invalidate entirely.

This does put the global invalidate under pgd_lock, but that shouldn't
matter.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Cc: Bin Yang <bin.yang@intel.com>
Cc: Mark Gross <mark.gross@intel.com>
Link: https://lkml.kernel.org/r/20180919085947.882287392@infradead.org