drm/amdgpu: update module paramter doc of amdgpu_dpm

the vega20 isn't supported swsmu.
Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -279,7 +279,7 @@ module_param_string(lockup_timeout, amdgpu_lockup_timeout, sizeof(amdgpu_lockup_
 /**
  * DOC: dpm (int)
  * Override for dynamic power management setting
- * (0 = disable, 1 = enable, 2 = enable sw smu driver for vega20)
+ * (0 = disable, 1 = enable)
  * The default is -1 (auto).
  */
 MODULE_PARM_DESC(dpm, "DPM support (1 = enable, 0 = disable, -1 = auto)");