Rename prime_raw_pkt to prime_raw_hid_pkt, and PRIME_RAW_DATA_SIZE to PRIME_RAW_HID_DATA_SIZE.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
Add hpcalcs_cable_get(), for obtaining the cable handle out of a calc handle.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>