greybus: loopback: add tracker variables to hold firmware timestamps

This patch adds tracker variables to hold the incoming firmware derived
timestamps where apbridge_latency_ts will contain the APBridge's view of
the UniPro turn-around time and gpbridge_latency_ts will contain the
GPBridge's view of it's own internal latency. Both values are reported
in microseconds.
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/loopback.c

@@ -83,6 +83,8 @@ struct gb_loopback {
 	u32 iteration_count;
 	u64 elapsed_nsecs;
 	u32 error;
+	u32 apbridge_latency_ts;
+	u32 gpbridge_latency_ts;
 };
 
 #define GB_LOOPBACK_FIFO_DEFAULT			8192