cmake: keep configure options naming in sync with autotools

In the cmake build system most configuration options are defined with a "DBUS_" prefix, e.g. DBUS_ENABLE_VERBOSE_MODE. The reason is probably that these variables are used in the dbus sources. To define these options when calling configure, option names beginning with '--enable_' are used, such as --enable-verbose-mode. This is used internally to create a variable called DBUS_ENABLE_VERBOSE_MODE, which is used in the source code and build system. It would help to analyze errors in the cmake build system if these definitions were more identical.