Cleanup unnecessary debugfs dentries and surrounding functions.

v3: remove return value check for debugfs_create_file()
v2: remove ttm_debugfs_entries array.
    do not init variables.
Signed-off-by: NNirmoy Das <nirmoy.das@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>