sysclk-lwla: Advertise SR_CONF_CONN option.
sysclk-lwla: Do not reset drv_context.instances on scan.

Apparently, frontends may call scan() more than once to accumulate
multiple devices, so do not reset the instance list pointer at the
start of each scan.  Also, number devices continuously across scans.
sysclk-lwla: Implement config_probe_set() callback.

Move setup of channels and trigger masks to the new probe
configuration callback.  Although the actual hardware setup
still happens just before acquisition, the new approach
already has the advantage that invalid settings are caught
early.
Also, it turns out that the LWLA1034 allows triggering on
channels which are not enabled for data acquisition.  This
feature is now supported as well.
sysclk-lwla: Implement config_commit() callback.

Move pre-acquisition hardware setup to the new config_commit()
callback.  At the moment, the only setting applied at commit
time is switching the clock source, which involves uploading
a new bitstream to the FPGA.