asm-generic/tlb: Track freeing of page-table directories in struct mmu_gather

asm-generic/tlb: Track freeing of page-table directories in struct mmu_gather

Some architectures require different TLB invalidation instructions
depending on whether it is only the last-level of page table being
changed, or whether there are also changes to the intermediate
(directory) entries higher up the tree.

Add a new bit to the flags bitfield in struct mmu_gather so that the
architecture code can operate accordingly if it's the intermediate
levels being invalidated.

Acked-by: Nicholas Piggin <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Will Deacon <[email protected]>