drivers: bluetooth: rpmsg: Send reset only when the Host is included

The rpmsg_close() call uses the HCI reset command to reset the
controller. But when building as controller-only we do not bring in the
infrastructure to send HCI commands (nor should we) and rpmsg_close()
will not be called anyway.

Fixes #63534.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>