Call initializecpucache() before ifuncs are resolved.

The function tweaks CPU capabilities based on the VM platform and
tunables, which affected selection of the cache flush method before
ifuncs were used, and should affect the cache flush in the same way
after ifunc.

PR: 232081
Reported by: phk
Analyzed by: avg
Sponsored by: The FreeBSD Foundation
Approved by: re (gjb)