uwb: order IEs by element ID

ECMA-368 requires that IEs in a beacon must be sorted by element ID.  Most
hardware uses the ordering in the Set IE URC command so get the ordering
right on the host.

Also refactor the IE management code:
  - use uwb_ie_next() instead of uwb_ie_for_each().
  - remove unnecessary functions.
  - API is now only uwb_rc_ie_add() and uwb_rc_ie_rm().

Signed-off-by: David Vrabel <david.vrabel@csr.com>