arm64: tlbflush: Ensure start/end of address range are aligned to stride

Since commit 3d65b6bb

 ("arm64: tlbi: Set MAX_TLBI_OPS to
PTRS_PER_PTE"), we resort to per-ASID invalidation when attempting to
perform more than PTRS_PER_PTE invalidation instructions in a single
call to __flush_tlb_range(). Whilst this is beneficial, the mmu_gather
code does not ensure that the end address of the range is rounded-up
to the stride when freeing intermediate page tables in pXX_free_tlb(),
which defeats our range checking.

Align the bounds passed into __flush_tlb_range().

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Reported-by: Hanjun Guo <guohanjun@huawei.com>
Tested-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>