Bluetooth: Change eir_has_data_type() to more generic eir_get_data()

To make the EIR parsing helper more general purpose, make it return
the found data and its length rather than just saying whether the data
was present or not.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>