Two fixes for the generic VDSO code which missed 5.5:

 - Make the update to the coarse timekeeper unconditional. This is required
   because the coarse timekeeper interfaces in the VDSO do not depend on a
   VDSO capable clocksource. If the system does not have a VDSO capable
   clocksource and the update is depending on the VDSO capable clocksource,
   the coarse VDSO interfaces would operate on stale data forever.

 - Invert the logic of __arch_update_vdso_data() to avoid further head
   scratching. Tripped over this several times while analyzing the update
   problem above.