uwb: add commands to add/remove IEs to the debug interface

Add the commands UWB_DBG_CMD_IE_ADD and UWB_DBG_CMD_IE_RM to the debug
interface and make them call uwb_rc_ie_add() and uwb_rc_ie_rm().

Signed-off-by: Stefano Panella <stefano.panella@csr.com>
Signed-off-by: David Vrabel <david.vrabel@csr.com>