powernv: Explicitly enable the facilities we support

Thus far we've relied on the firmware setting HFSCR correctly, enabling
all facilities. However, it appears some recent firmwares do not.
Linux explicitly enables all facilities it supports (including
transactional memory, which new firmwares apparently do not enable), so
do the same here, explicitly enable all the facilities FreeBSD supports.

MFC after: 1 week

(cherry picked from commit fe73eb441f1c98fe350f4822c7d2abfeef046bf8)