dt-bindings: spi: Move the bindings for the FSL QSPI driver

Move the documentation of the old SPI NOR driver to the place of the new
SPI memory interface based driver.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>