ARM: dts: MSM8974: Add pinctrl node

Add the pin control node and pin definitions of SPI8.

Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kumar Gala <galak@codeaurora.org>