b210: Lock dual-channel tuning access
b210: Lock dual-channel tuning access

Frequency tuning is a multi-step process with RF and DDC/DUC protoimns
that can be corrupted if both channels attempt to tune at the same time.

Signed-off-by: Tom Tsou <96835dd8bfa718bd6447ccc87af89ae1675daeca@tsou.cc>

osmocom/osmo-trx,osmocom/osmo-trx,pothosware/osmo-trx,kkroo/osmo-trx,pothosware/osmo-trx,osmocom/osmo-trx,kkroo/osmo-trx,ttsou/osmo-trx,ttsou/osmo-trx,pothosware/osmo-trx,kkroo/osmo-trx,kkroo/osmo-trx,pothosware/osmo-trx,osmocom/osmo-trx,ttsou/osmo-trx,ttsou/osmo-trx