KVM: selftests: restore special vmmcall code layout needed by the harness

KVM: selftests: restore special vmmcall code layout needed by the harness

Commit 8fda37cf3d41 ("KVM: selftests: Stuff RAX/RCX with 'safe' values
in vmmcall()/vmcall()", 2022-11-21) broke the svm_nested_soft_inject_test
because it placed a "pop rbp" instruction after vmmcall.  While this is
correct and mimics what is done in the VMX case, this particular test
expects a ud2 instruction right after the vmmcall, so that it can skip
over it in the L1 part of the test.

Inline a suitably-modified version of vmmcall() to restore the
functionality of the test.

Fixes: 8fda37cf3d41 ("KVM: selftests: Stuff RAX/RCX with 'safe' values in vmmcall()/vmcall()"
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20221130181147.9911-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>