Altera QUADSPI driver

Required properties:
- compatible: Should be "altr,quadspi-1.0"
- reg: Address and length of the register set  for the device. It contains
  the information of registers in the same order as described by reg-names
- reg-names: Should contain the reg names
  "avl_csr": Should contain the register configuration base address
  "avl_mem": Should contain the data base address
- #address-cells: Must be <1>.
- #size-cells: Must be <0>.
- flash device tree subnode, there must be a node with the following fields:
	- compatible: Should contain the flash name:
	  1. EPCS:   epcs16, epcs64, epcs128
	  2. EPCQ:   epcq16, epcq32, epcq64, epcq128, epcq256, epcq512, epcq1024
	  3. EPCQ-L: epcql256, epcql512, epcql1024
	- #address-cells: please refer to /mtd/partition.txt
	- #size-cells: please refer to /mtd/partition.txt
	For partitions inside each flash, please refer to /mtd/partition.txt

Example:

	quadspi_controller_0: quadspi@0x180014a0 {
		compatible = "altr,quadspi-1.0";
		reg = <0x180014a0 0x00000020>,
		      <0x14000000 0x04000000>;
		reg-names = "avl_csr", "avl_mem";
		#address-cells = <1>;
		#size-cells = <0>;
		flash0: epcq512@0 {
			compatible = "altr,epcq512";
			#address-cells = <1>;
			#size-cells = <1>;
		};
	};
