Bluetooth: hci_bcm: Drive RTS only for BCM43438

The commit 3347a809 ("Bluetooth: hci_bcm: Fix RTS handling during
startup") is causing at least a regression for AP6256 on Orange Pi 3.
So do the RTS line handing during startup only on the necessary platform.

Fixes: 3347a809

 ("Bluetooth: hci_bcm: Fix RTS handling during startup")
Reported-by: Ondřej Jirman <megous@megous.com>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>