or just offering info. In the former case, we don't probe/attach to allow
the ACPI driver precedence. A refinement of this would be to actually
use the info provided by acpi_perf(4) to get the real CPU clock rates
instead of estimating them but since all systems that support both
acpi_perf(4) and ichss(4) export the control registers to acpi_perf(4),
it can just handle the registers on its own.