KVM: x86: Use common definition for kvm_nested_vmexit tracepoint

Use the newly introduced TRACE_EVENT_KVM_EXIT to define the guts of
kvm_nested_vmexit so that it captures and prints the same information as
kvm_exit.  This has the bonus side effect of fixing the interrupt info
and error code printing for the case where they're invalid, e.g. if the
exit was a failed VM-Entry.  This also sets the stage for retrieving
EXIT_QUALIFICATION and VM_EXIT_INTR_INFO in nested_vmx_reflect_vmexit()
if and only if the VM-Exit is being routed to L1.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923201349.16097-7-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>