gpu: nvgpu: enhance pbus error reporting

-Dump timeout save0 and save1 even if they could
 be unreliable when fecs_tgt in set in save0 . This
 is good to have for debug purposes.
-Add priv_ring hal for decode_error_code
-Decode fecs error code for supported error types

Bug 1998067

Change-Id: I60cb6902d099df4a7df45fa624e44d9e0d46360f
Signed-off-by: Seema Khowala <seemaj@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1683014
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/gk20a/gk20a.h

@@ -1113,6 +1113,7 @@ struct gpu_ops {
 	} falcon;
 	struct {
 		void (*isr)(struct gk20a *g);
+		void (*decode_error_code)(struct gk20a *g, u32 error_code);
 	} priv_ring;
 	struct {
 		int (*check_priv_security)(struct gk20a *g);