drm/amdgpu/psp: use define rather than magic number for mode1 reset

Use the define rather than hardcoded value.

Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>