Cortex A9 private timer

[Aymeric Vincent <aymericvincent%free.fr@localhost>]

Hi,

the addition of a9ptmr support breaks at least the DE0 Nano SoC port
(Cortex A9) because both a9tmr and a9ptmr are enabled. The kernel hangs
during boot in what looks like an interrupt storm but I didn't
investigate much. A workaround for me is to disable a9ptmr in the dtb
but I fail to see the intent of making a private timer the one
reponsible for calling hardclock().

So far, we had a9tmr on Cortex A5/A9 and gtmr on other Cortex. They both
call hardclock() and don't collide because no SoC can provide both so
only one will attach at runtime.

I see that the meson platform mandates the use of a9ptmr_delay, so there
is certainly a reason for this support but it breaks other ports and was
pulled up to netbsd-9 very quickly... :-/ May I ask for a little
explanation?

Regards,
 Aymeric