DBus: Refactor array adding, add binary arrays

DBus: Refactor array adding, add binary arrays

Some new code we're working on will require the dbus type "aay" (an
array of arrays of bytes). To add this, refactor the array code to
reduce code duplication by given a type string to the array starting
code, and also add code to create and parse such arrays from or into an
array of struct wpabuf respectively.

Since there's no unique DBus type for this, add a "fake"
WPAS_DBUS_TYPE_BINARRAY type that is separate from the regular DBus
types for parsing.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>