Bluetooth: hci_uart: Disable HCI ECC commands temporarily

HCI ECC commands are causing freezes in the controller build. Until
further investigation is done disable them to avoid issues when running
the controller standalone.

Change-id: Ifab0fa362348b72e88adaa5250c914770e4a70ba
Signed-off-by: Vinayak Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>