doc: releases: release-notes: 3.7: can_get_{min,max}_bitrate() changes

Mention the new can_get_bitrate_min() and can_get_bitrate_max() CAN
controller API functions along with the deprecating of the existing
can_get_min_bitrate() and can_get_max_bitrate().

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>