SVGHMI: Stop ignoring HMI_NODE in HMI tree, and count it as a BOOL. Soon we use those nodes as reference for relative page jump, and as an "enable" bit for features associated to an HMI tree fragment.

                  <xsd:element name="Linux">
                    <xsd:complexType>
                      %(toolchain_gcc)s
                    </xsd:complexType>
                  </xsd:element>