drm/amdgpu/pm: Remove redundant generic message index

Remove SMU_MSG_GfxDriverReset generic index.
Always use SMU_MSG_GfxDeviceDriverReset as the generic index for reset.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>