KVM x86 fixes for 6.8:

 - Make a KVM_REQ_NMI request while handling KVM_SET_VCPU_EVENTS if and only
   if the incoming events->nmi.pending is non-zero.  If the target vCPU is in
   the UNITIALIZED state, the spurious request will result in KVM exiting to
   userspace, which in turn causes QEMU to constantly acquire and release
   QEMU's global mutex, to the point where the BSP is unable to make forward
   progress.

 - Fix a type (u8 versus u64) goof that results in pmu->fixed_ctr_ctrl being
   incorrectly truncated, and ultimately causes KVM to think a fixed counter
   has already been disabled (KVM thinks the old value is '0').

 - Fix a stack leak in KVM_GET_MSRS where a failed MSR read from userspace
   that is ultimately ignored due to ignore_msrs=true doesn't zero the output
   as intended.