drm/amd/pm: fixes a random hang in S4 for SMU v13.0.4/11

While doing multiple S4 stress tests, GC/RLC/PMFW get into
an invalid state resulting into hard hangs.

Adding a GFX reset as workaround just before sending the
MP1_UNLOAD message avoids this failure.

Signed-off-by: Tim Huang <Tim.Huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>