keymaster: add 4.0 to compatibility matrix

    <hal format="hidl" optional="false">

        <name>android.hardware.keymaster</name>

        <version>3.0</version>

        <version>4.0</version>

        <interface>

            <name>IKeymasterDevice</name>

            <instance>default</instance>

	    <!-- TODO: strongbox here? -->

        </interface>

    </hal>

    <hal format="hidl" optional="true">