dt-bindings: sdhci-of-at91: new compatible string and update properties

sdhci-of-at91 driver.

Required properties:

- compatible:		Must be "atmel,sama5d2-sdhci".

- compatible:		Must be "atmel,sama5d2-sdhci" or "microchip,sam9x60-sdhci".

- clocks:		Phandlers to the clocks.

- clock-names:		Must be "hclock", "multclk", "baseclk";

- clock-names:		Must be "hclock", "multclk", "baseclk" for

			"atmel,sama5d2-sdhci".

			Must be "hclock", "multclk" for "microchip,sam9x60-sdhci".

Optional properties:

- assigned-clocks:	The same with "multclk".

- assigned-clock-rates	The rate of "multclk" in order to not rely on the

			gck configuration set by previous components.

- microchip,sdcal-inverted: when present, polarity on the SDCAL SoC pin is

  inverted. The default polarity for this signal is described in the datasheet.

  For instance on SAMA5D2, the pin is usually tied to the GND with a resistor

Example:

sdmmc0: sdio-host@a0000000 {

mmc0: sdio-host@a0000000 {

	compatible = "atmel,sama5d2-sdhci";

	reg = <0xa0000000 0x300>;

	interrupts = <31 IRQ_TYPE_LEVEL_HIGH 0>;

	clocks = <&sdmmc0_hclk>, <&sdmmc0_gclk>, <&main>;

	clock-names = "hclock", "multclk", "baseclk";

	assigned-clocks = <&sdmmc0_gclk>;

	assigned-clock-rates = <480000000>;

};