drm/amdkfd: Track SDMA utilization per process

Track SDMA usage on a per process basis and report it through sysfs.
The value in the sysfs file indicates the amount of time SDMA has
been in-use by this process since the creation of the process.
This value is in microsecond granularity.

Signed-off-by: Mukul Joshi <mukul.joshi@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>