kvmclock: Always register type

Currently, the "kvmclock" type is only registered when kvm_enabled().

This breaks when moving type registration to before command line
parsing (so that QOM types can be used for CPU and machine).

Since the QOM classes are lazy-initialized anyway and kvmclock_create()
has another kvm_enabled() check, simply drop the KVM check in
kvmclock_register_types().

kvm-i8259, kvm-apic and kvm-ioapic do not suffer from such a check.

Reviewed-by: please.
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
