KVM SVM changes for 6.12:

 - Don't stuff the RSB after VM-Exit when RETPOLINE=y and AutoIBRS is enabled,
   i.e. when the CPU has already flushed the RSB.

 - Trace the per-CPU host save area as a VMCB pointer to improve readability
   and cleanup the retrieval of the SEV-ES host save area.

 - Remove unnecessary accounting of temporary nested VMCB related allocations.