HAL_PX4: handle IO errors on microsd

this should handle EINTR gracefully
HAL_PX4: added UART performance counters
HAL_PX4: added storage performance counters
HAL_PX4: added scheduler performance counters
HAL_PX4: prevent loop() overruns using hrt

this ensures if loop() takes more than 1 second, the main task gets
its priority dropped until loop() completes