Add Yi and Zi to prefixes

[Intelligent2013]

In UnitsML schema there are prefixes

<xsd:attribute name="prefix">
    <xsd:annotation>
        <xsd:documentation>Prefix identifier; e.g., m, k, M, G.  [Enumeration order is by prefix magnitude (Y to y) followed by binary prefixes.]</xsd:documentation>
    </xsd:annotation>
    <xsd:simpleType>
        <xsd:restriction base="xsd:token">
            <xsd:enumeration value="Y"/>
            <xsd:enumeration value="Z"/>
            <xsd:enumeration value="E"/>
            <xsd:enumeration value="P"/>
            <xsd:enumeration value="T"/>
            <xsd:enumeration value="G"/>
            <xsd:enumeration value="M"/>
            <xsd:enumeration value="k"/>
            <xsd:enumeration value="h"/>
            <xsd:enumeration value="da"/>
            <xsd:enumeration value="d"/>
            <xsd:enumeration value="c"/>
            <xsd:enumeration value="m"/>
            <xsd:enumeration value="u"/>
            <xsd:enumeration value="n"/>
            <xsd:enumeration value="p"/>
            <xsd:enumeration value="f"/>
            <xsd:enumeration value="a"/>
            <xsd:enumeration value="z"/>
            <xsd:enumeration value="y"/>
            <xsd:enumeration value="Ki"/>
            <xsd:enumeration value="Mi"/>
            <xsd:enumeration value="Gi"/>
            <xsd:enumeration value="Ti"/>
            <xsd:enumeration value="Pi"/>
            <xsd:enumeration value="Ei"/>
            <xsd:enumeration value="Zi"/>
            <xsd:enumeration value="Yi"/>
        </xsd:restriction>
    </xsd:simpleType>
</xsd:attribute>

In prefixes.yaml there are all values except Yi and Zi. As we'll generate xsd on-fly based on unitsdb values, need to add these prefixes.

[ronaldtse]

Agree. From SI Brochure 9e: