Move the code to update cpu_cx_count out of acpi_cpu_generic_cx_probe() and
into acpi_cpu_startup() which is where all the other code to update this
global variable lives. This fixes a bug where cpu_cx_count was not updated
correctly if acpi_cpu_generic_cx_probe() returned early.

PR: kern/108581
Debugged by: Bruce Cran
Reviewed by: avg, njl, sepotvin
MFC after: 3 days