This is based on the amd64 implementation. Support for both PLT and
non-PLT (e.g. a global variable initilised with a pointer to an ifunc)
cases are supported.
We don't pass anything to the resolver as it is expected they will read
the ID registers directly, with the number of registers with CPU info
likely to increase in the future.
Reviewed by: kib
Approved by: re (gjb)
Differential Revision: https://reviews.freebsd.org/D17341
6e4fdb5c9d