This adds the Quad SPI controller to the main sdm845 device tree file.
Boards will be expected to assign the proper pinctrl depending on how
many chip selects they have hooked up and how many data lines.

This depends on commit 48735597 ("clk: qcom: Add qspi (Quad SPI)
clock defines for sdm845 to header") to add the needed defines.  It
also shouldn't land until the patch ("dt-bindings: spi: Qualcomm Quad
SPI(QSPI) documentation") [1] lands.

[1] https://lkml.kernel.org/r/20181002214709.162330-1-ryandcase@chromium.orgReviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>