This patch adds support for HOST OpenThread communication to the RCP
co-processor via UART using SPINEL protocol.
The aim is to use OpenThread's RCP (Radio Co-Processor) with HOST device
(for example imxRT1020). Such configuration is the same as one used
with PC program (ot-cli) and RCP.
Signed-off-by: Lukasz Majewski <lukma@denx.de>
