Qualcomm Serial Peripheral Interface (SPI)

Required properties:
- compatible : should be "qcom,spi-qup-v2".
- reg : offset and length of the QUP register map.
- interrupts : should contain the QUP core interrupt.
- spi-max-frequency : specifies maximum SPI clock frequency, Units - Hz.

Optional properties:
- gpios : specifies the gpio pins to be used for SPI CLK, MISO, MOSI in
  that order.
- cs-gpios : specifies the gpio pins to be used for chipselects.

SPI slave nodes must be children of the SPI master node and contain
the following properties.
- reg : (required) chip select address of device.
- compatible : (required) name of SPI device following generic names
  recommended practice
- spi-max-frequency : (required) Maximum SPI clocking speed of device in Hz
- interrupts : (recommended) should contain the SPI slave interrupt number
  encoded depending on the type of the interrupt controller.
- interrupt-parent : (recommended) the phandle for the interrupt controller
  that services interrupts for this device.
- spi-cpol : (optional) Empty property indicating device requires inverse
  clock polarity (CPOL) mode
- spi-cpha : (optional) Empty property indicating device requires shifted
  clock phase (CPHA) mode
- spi-cs-high : (optional) Empty property indicating device requires
  chip select active high

Example:
	spi@f9924000 {
		compatible = "qcom,spi-qup-v2";
		reg = <0xf9924000 0x1000>;
		interrupts = <0 96 0>;
		spi-max-frequency = <24000000>;
		#address-cells = <1>;
		#size-cells = <0>;

		device@0 {
			compatible = "spidev";
			reg = <0>;
			spi-max-frequency = <5000000>;
		};
	};

