bus: Activate INTRNG interrupts in common code

[andrew]

Summary

We need to call into INTRNG to activate an interrupt on platforms that
use it. When bus_generic_rman_activate_resource was added. As this
is only a problem for buses that manage their own IRQ space this was
only a problem for gpiobus as it creates interrupts for each GPIO pin.

Reported by: cperciva
Sponsored by: Arm Ltd

[jhb]

The commit log doesn't read quite correct. I would suggest something like:

We need to call into INTRNG to activate all interrupts on platforms that
use it.  Currently, interrupts are only activated in the nexus drivers for
INTRNG platforms, but this does not handle other bus devices such as
gpiobus that manage their own IRQ space.

[cperciva]

This + D47253 makes EC2's GPIO "power button" work for me. Please commit (and MFC soon)!

[cperciva]

In D47282#1079088, @cperciva wrote:

This + D47253 makes EC2's GPIO "power button" work for me. Please commit (and MFC soon)!

Looks like the MFC isn't entirely trivial due to a bunch of changes @jhb has made since stable/14 branched. John, am I right in thinking that your changes in subr_bus.c won't be landing in stable/14?

[jhb]

I am not planning to merge for 14.2, no. There were many changes tied up in the refactoring of the bus resource management in 15.