drm/amdgpu: Add show_fdinfo() interface

Tracking devices, process info and fence info using
/proc/pid/fdinfo

Signed-off-by: David M Nieto <David.Nieto@amd.com>
Signed-off-by: Roy Sun <Roy.Sun@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210426062701.39732-2-Roy.Sun@amd.com