accel/ivpu: Share NPU busy time in sysfs

accel/ivpu: Share NPU busy time in sysfs

The driver tracks the time spent by NPU executing jobs
and shares it through sysfs `npu_busy_time_us` file.
It can be then used by user space applications to monitor device
utilization.

NPU is considered 'busy' starting with a first job submitted
to firmware and ending when there is no more jobs pending/executing.

Signed-off-by: Tomasz Rusinowicz <tomasz.rusinowicz@intel.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240513120431.3187212-13-jacek.lawrynowicz@linux.intel.com