* Exynos DWC_mobile_storage

The Exynos provides DWC_mobile_storage interface which supports
. Embedded Multimedia Cards (EMMC-version 4.5)
. Secure Digital memory (SD mem-version 2.0)
. Secure Digital I/O (SDIO-version 3.0)
. Consumer Electronics Advanced Transport Architecture (CE-ATA-version 1.1)

The Exynos DWC_mobile_storage provides four channels.
SOC specific and Board specific properties are channel specific.

Required SoC Specific Properties:

- compatible: should be
	- samsung,exynos-dwmmc: for exynos platforms

- reg: physical base address of the controller and length of memory mapped
	region.

- interrupts: The interrupt number to the cpu.

Required Board Specific Properties:

- #address-cells: should be 1.
- #size-cells: should be 0.
- samsung,bus-width: The width of the bus used to interface the devices
	supported by DWC_mobile_storage (SD-MMC/EMMC/SDIO).
	. Typically the bus width is 4 or 8.
- samsung,timing: The timing values to be written into the
	Drv/sample clock selection register of corresponding channel.
	. It is comprised of 3 values corresponding to the 3 fileds
	  'SelClk_sample', 'SelClk_drv' and 'DIVRATIO' of CLKSEL register.
	. SelClk_sample: Select sample clock among 8 shifted clocks.
	. SelClk_drv: Select drv clock among 8 shifted clocks.
	. DIVRATIO: Clock Divide ratio select.
	. The above 3 values are used by the clock phase shifter.

Example:

mmc@12200000 {
	samsung,bus-width = <8>;
	samsung,timing = <1 3 3>;
	samsung,removable = <1>;
}
In the above example,
	. The bus width is 8
	. Timing is comprised of 3 values as explained below
		1 - SelClk_sample
		3 - SelClk_drv
		3 - DIVRATIO
	. The 'removable' flag indicates whether the the particilar device
	  cannot be removed (always present) or it is a removable device.
		1 - Indicates that the device is removable.
		0 - Indicates that the device cannot be removed.
