Bluetooth: Use BT_BYTES_LIST_LEXX macros for encoding of data

Modify the BT_UUID_XX_ENCODE and BT_LE_SUPP_FEAT_XX_ENCODE
macros to use the SYS_ENCODE_LEXX macros, instead of re-inventing
the encoding.

Also apply the macros for several other places.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>