mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free_pgtables()

mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free_pgtables()

Commit b67fbebd4cf9 ("mmu_gather: Force tlb-flush VM_PFNMAP vmas") added a
forced tlbflush to tlb_vma_end(), which is required to avoid a race
between munmap() and unmap_mapping_range().  However it added some
overhead to other paths where tlb_vma_end() is used, but vmas are not
removed, e.g.  madvise(MADV_DONTNEED).

Fix this by moving the tlb flush out of tlb_end_vma() into
free_pgtables(), somewhat similar to the stable version of the original
commit: e.g.  stable commit 895428ee124a ("mm: Force TLB flush for PFNMAP
mappings before unlink_file_vma()").

Note, that if tlb->fullmm is set, no flush is required, as the whole mm is
about to be destroyed.

Link: https://lkml.kernel.org/r/20250127195321.35779-1-roman.gushchin@linux.dev
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Jann Horn <jannh@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>