KVM fixes for 6.7-rcN:

 - When checking if a _running_ vCPU is "in-kernel", i.e. running at CPL0,
   get the CPL directly instead of relying on preempted_in_kernel, which
   is valid if and only if the vCPU was preempted, i.e. NOT running.

 - Set .owner for various KVM file_operations so that files refcount the
   KVM module until KVM is done executing _all_ code, including the last
   few instructions of kvm_put_kvm().  And then revert the misguided
   attempt to rely on "struct kvm" refcounts to pin KVM-the-module.

 - Fix a benign "return void" that was recently introduced.