mtd: spi-nor: Add driver for Cadence Quad SPI Flash Controller

Add support for the Cadence QSPI controller. This controller is
present in the Altera SoCFPGA SoCs and this driver has been tested
on the Cyclone V SoC.

Signed-off-by: Graham Moore <grmoore@opensource.altera.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alan Tull <atull@opensource.altera.com>
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Graham Moore <grmoore@opensource.altera.com>
Cc: Vignesh R <vigneshr@ti.com>
Cc: Yves Vandervennet <yvanderv@opensource.altera.com>
Cc: devicetree@vger.kernel.org
Signed-off-by: Brian Norris <computersforpeace@gmail.com>