arm64: dts: qcom: 8x16: UART1 add CTS_N, RTS_N pin configurations

Add devicetree bindings for UART1 CTS_N and RTS_N pins.

Signed-off-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>
Signed-off-by: Andy Gross <agross@codeaurora.org>