* Freescale Low Power SPI (LPSPI) for i.MX

Required properties:
- compatible :
  - "fsl,imx7ulp-spi" for LPSPI compatible with the one integrated on i.MX7ULP soc
  - "fsl,imx8qxp-spi" for LPSPI compatible with the one integrated on i.MX8QXP soc
- reg : address and length of the lpspi master registers
- interrupt-parent : core interrupt controller
- interrupts : lpspi interrupt
- clocks : lpspi clock specifier. Its number and order need to correspond to the
	   value in clock-names.
- clock-names : Corresponding to per clock and ipg clock in "clocks"
		respectively. In i.MX7ULP, it only has per clk, so use CLK_DUMMY
		to fill the "ipg" blank.
- spi-slave : spi slave mode support. In slave mode, add this attribute without
	      value. In master mode, remove it.

Examples:

lpspi2: lpspi@40290000 {
	compatible = "fsl,imx7ulp-spi";
	reg = <0x40290000 0x10000>;
	interrupt-parent = <&intc>;
	interrupts = <GIC_SPI 28 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clks IMX7ULP_CLK_LPSPI2>,
		 <&clks IMX7ULP_CLK_DUMMY>;
	clock-names = "per", "ipg";
	spi-slave;
};