cputlb: Hoist timestamp outside of loops over tlbs

cputlb: Hoist timestamp outside of loops over tlbs

Do not call get_clock_realtime() in tlb_mmu_resize_locked,
but hoist outside of any loop over a set of tlbs.  This is
only two (indirect) callers, tlb_flush_by_mmuidx_async_work
and tlb_flush_page_locked, so not onerous.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>