The UART in PSoC is based on an 8 bit digital block. Because of this it is not possible to transmit 7 data bits and one parity bit in hardware. But this can be achieved in firmware. Configure the UART with no parity. Construct a byte with 7 data bits and use the 8th bit for parity. The parity bit has to be calculated in firmware and has to be set or cleared accordingly. Now send this byte over the UART.