coresight: sysfs: Increment refcount only for software source

coresight: sysfs: Increment refcount only for software source

Except for software sources (e.g. STM), other sources treat multiple
enables as equivalent to a single enable. The device mode already
tracks the binary state, so it is redundant to operate refcount.

Introduce a helper coresight_is_software_source() for check software
source. Refactor to maintain the refcount only for software sources.
This simplifies future CPU PM handling without refcount logic.

Tested-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: Jie Gan <jie.gan@oss.qualcomm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20260515-arm_coresight_path_power_management_improvement-v14-26-f88c4a3ecfe9@arm.com