* Introduce mbus_data_bcd_decode_hex
The convert function mbus_data_bcd_decode (BCD to decimal) suffers from
information loss in case of hexacimal digits. So introduce a new function
mbus_data_bcd_decode_hex (BCD to hexadecimal), which isn't affected and
use this for default XML output. But keep mbus_data_bcd_decode for
normalized output.
