coresight: remove the unnecessary function coresight_is_bit_set()

This function coresight_is_bit_set() isn't called, so we should
remove it.

Signed-off-by: Kaixu Xia <xiakaixu@huawei.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>