drivers: can: deprecate can_write() API wrapper function

Deprecate the can_write() API wrapper function in favor of using
can_send() directly.

The can_write() API wrapper function:
- Does not support CAN-FD data lengths.
- Auto-selects between standard/extended CAN identifiers based on the
  CAN ID (something which should be selected by the caller as the
  selection affects filters on the receiving end).
- Does not support callbacks for frame transmission results.
- Has no in-tree users.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>