Allow to build coresight-cti as a module, for ease of development.

- Kconfig becomes a tristate, to allow =m
- append -core to source file name to allow module to
  be called coresight-cti by the Makefile
- add an cti_remove function, for module unload
- add a MODULE_DEVICE_TABLE for autoloading on boot
- move cti_remove_conn_xrefs to cti_remove since all sysfs links
  have gone when system calls device_release.

Reviewed-by Mike Leach <mike.leach@linaro.org>
Tested-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200928163513.70169-22-mathieu.poirier@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>