spi: Introduce new driver for Qualcomm QuadSPI controller

New driver for Qualcomm QuadSPI(QSPI) controller that is used to
communicate with slaves such as flash memory devices. The QSPI controller
can operate in 2 or 4 wire mode but only supports SPI Mode 0. The
controller can also operate in Single or Dual data rate modes.

Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>
Signed-off-by: Ryan Case <ryandcase@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>