KVM: Portability: Combine kvm_init and kvm_init_x86

Will be called once arch module registers itself.

Signed-off-by: Zhang Xiantao <xiantao.zhang@intel.com>
Acked-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>