drm/amdgpu/vcn: reset fw_shared when VCPU buffers corrupted on vcn v4.0.3

It is not necessarily corrupted. When there is RAS fatal error, device
memory access is blocked. Hence vcpu bo cannot be saved to system memory
as in a regular suspend sequence before going for reset. In other full
device reset cases, that gets saved and restored during resume.

v2: Remove redundant code like vcn_v4_0 did
v2: Refine commit message
v3: Drop the volatile
v3: Refine commit message

Signed-off-by: Xiang Liu <xiang.liu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Stanley.Yang <Stanley.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>