PPC64: use hwref instead of cpuid
On CHRP and PowerNV, use the interrupt server number in the cpuref and pcpu
hwref field instead of the device-tree phandle and make the CPU IDs reported
to the scheduler dense and with the BSP at 0.
Submitted by: Wojciech Macek <wma@semihalf.com>
Obtained from: Semihalf
Sponsored by: IBM, QCM Technologies
Differential revision: https://reviews.freebsd.org/D14011