To fix the powerpc build, back out r331184, which was this mfc:

MFC r326859:

Add identifier for POWER9 CPU to CPU list

Without the identifier in the list booting FreeBSD results in printing the
following (from a PowerKVM boot):

cpu0: Unknown PowerPC CPU revision 0x1201, 2550.00 MHz

For now, add the same feature list as POWER8. As new capabilities are added to
support POWER9 specific features, they will be added to this.

PR: 224344