ARM: dts: apq8064: Add DT support for GSBI6 and for UART pin mux

This change adds DT support for GSBI6 and muxes the gpio pins
as UART lines. Also defines a alias for serial port on these lines.

Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>
[Srinivas Kandagatla]: fix pinctrl location and rename alias correctly
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <agross@codeaurora.org>