drm/amdkfd: Add some eveiction debugging code

Extending the module parameter debug_evictions to also print a stack
trace when the eviction code path is called.

Signed-off-by: Philip Cox <Philip.Cox@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>