Add minOccurs="0"

For privapp-permissions and oem-permissions elements, some xml files
don't need to permission and deny-permission properties. So add the
minOccurs="0" for these elements.

Test: vts-tradefed run vts -m VtsValidatePermission
Bug: 143251304
Change-Id: Ib93a40e646f9c65bd62d23396c12ea31f2d735d8