TI QSPI controller.

Required properties:
- compatible : should be "ti,dra7xxx-qspi" or "ti,am4372-qspi".
- reg: Should contain QSPI registers location and length.
- reg-names: Should contain the resource reg names.
	- qspi_base: Qspi configuration register Address space
	- qspi_mmap: Memory mapped Address space
	- (optional) qspi_ctrlmod: Control module Address space
- interrupts: should contain the qspi interrupt number.
- #address-cells, #size-cells : Must be present if the device has sub-nodes
- ti,hwmods: Name of the hwmod associated to the QSPI

Recommended properties:
- spi-max-frequency: Definition as per
                     Documentation/devicetree/bindings/spi/spi-bus.txt

Example:

qspi: qspi@4b300000 {
	compatible = "ti,dra7xxx-qspi";
	reg = <0x47900000 0x100>, <0x30000000 0x3ffffff>;
	reg-names = "qspi_base", "qspi_mmap";
	#address-cells = <1>;
	#size-cells = <0>;
	spi-max-frequency = <25000000>;
	ti,hwmods = "qspi";
};
