drivers: serial: CAT1 UART driver: fix HW flow control

fix HW flow control:
- remove cyhal_uart_enable_flow_control
- added Cy_SCB_UART_EnableCts if cfg->flow_ctrl = true
  (required to enable hw flow control)
- configuration of CTS/RTS done by pincntr driver

Signed-off-by: Nazar Palamar <nazar.palamar@infineon.com>