qemu: domain: Add new function to set up encrypted secrets only
qemu: domain: Add new function to set up encrypted secrets only

Some code paths can't use the unencrypted secret. Add a helper which
checks and sets up an encrypted secret only and reuse it when setting up
the secret to decrypt the TLS private key in qemuDomainSecretInfoTLSNew.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

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