coresight-etm: remove check for unknown Kconfig macro

The CoreSight ETM/PTM driver contains a check for a
CONFIG_CORESIGHT_SOURCE_ETM_DEFAULT_ENABLE macro. But there's no related
Kconfig symbol CORESIGHT_SOURCE_ETM_DEFAULT_ENABLE. Remove that check
and the single line of code it hides.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>