intr/powerpc: update 0c50edff52f2 hack

[ehem_freebsd_m5p.com]

Summary

Modifying the ->ie_post_filter hook of an interrupt event is
troublesome. While they are intimately tied to the machine interrupt
frameworks, this modification is particularly troublesome. In
particular there is hope to remove this ability in the future.

[ehem_freebsd_m5p.com]

Updating to jhibbits@ preferred method of accomplishing the goal. This is only expected to be used during a transition period, so hopefully will disappear later.

[ehem_freebsd_m5p.com]

Closing in light of rG:700f7e793b3793606fbb9942eda03ac02991c126.