Turns out the integration of the GIC-500 on the Rockchip RK3399 is busted.

Turns out the integration of the GIC-500 on the Rockchip RK3399 is busted.
It treats all access to the memory mapped registers as "secure" even if
we're running in non-secure mode.  As a result, during bringup of OpenBSD
on the RK3399, I got confused and tweaked the interrupt priorities in a way
that is wrong (but worked on the RK3399.

Fix those priorities to match what they should be according to the
documentation (and works on other hardware that includes a GICv3) and
add code that detects the broken RK3399 GIC and adjusts the priorities
accordingly.  Also remove (broken) code that tries to mess around with
group 0 interrupts and fix setting bits in the GICD_CTLR register on the
broken RK3399 GIC.