* STMicroelectronics Quad Serial Peripheral Interface(QSPI)

Required properties:
- compatible: should be "st,stm32f469-qspi"
- reg: the first contains the register location and length.
       the second contains the memory mapping address and length
- reg-names: should contain the reg names "qspi" "qspi_mm"
- interrupts: should contain the interrupt for the device
- clocks: the phandle of the clock needed by the QSPI controller
- A pinctrl must be defined to set pins in mode of operation for QSPI transfer

Optional properties:
- resets: must contain the phandle to the reset controller.

A spi flash (NOR/NAND) must be a child of spi node and could have some
properties. Also see jedec,spi-nor.txt.

Required properties:
- reg: chip-Select number (QSPI controller may connect 2 flashes)
- spi-max-frequency: max frequency of spi bus

Optional properties:
- spi-rx-bus-width: see ./spi-bus.txt for the description
- dmas: DMA specifiers for tx and rx dma. See the DMA client binding,
Documentation/devicetree/bindings/dma/dma.txt.
- dma-names: DMA request names should include "tx" and "rx" if present.

Example:

qspi: spi@a0001000 {
	compatible = "st,stm32f469-qspi";
	reg = <0xa0001000 0x1000>, <0x90000000 0x10000000>;
	reg-names = "qspi", "qspi_mm";
	interrupts = <91>;
	resets = <&rcc STM32F4_AHB3_RESET(QSPI)>;
	clocks = <&rcc 0 STM32F4_AHB3_CLOCK(QSPI)>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_qspi0>;

	flash@0 {
		compatible = "jedec,spi-nor";
		reg = <0>;
		spi-rx-bus-width = <4>;
		spi-max-frequency = <108000000>;
		...
	};
};