target/i386: allow reordering max_x86_cpu_initfn vs accel CPU init

target/i386: allow reordering max_x86_cpu_initfn vs accel CPU init

The PMU feature is only supported by KVM, so move it there.  And since
all accelerators other than TCG overwrite the vendor, set it in
max_x86_cpu_initfn only if it has not been initialized by the
superclass.  This makes it possible to run max_x86_cpu_initfn
after accelerator init.

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>