The SMP pin can be left floating, or grounded if not in use. If the SMP is not being used it can be turned off in the Chip Editor View. The option to switch OFF the SMP is available in the global parameters.
Grounding the SMP pin will do nothing because the SMP pin is connected to a (PSoC internal) open drain FET. When the FET is turned On, the pin is connected to ground. When the FET is off, the pin is high impedence. Connecting the high impedance pin to ground will do nothing.