Implement function psp_gfx_cmd_name to show cmd name
via cmd id.

v2: rename it to psp_gfx_cmd_name
Signed-off-by: NLang Yu <Lang.Yu@amd.com>
Reviewed-by: NHuang Rui <ray.huang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>