Spreadtrum ADI controller

ADI is the abbreviation of Anolog-Digital interface, which is used to access
analog chip (such as PMIC) from digital chip. ADI controller follows the SPI
framework for its hardware implementation is alike to SPI bus and its timing
is compatile to SPI timing.

ADI controller has 50 channels including 2 software read/write channels and
48 hardware channels to access analog chip. For 2 software read/write channels,
users should set ADI registers to access analog chip. For hardware channels,
we can configure them to allow other hardware components to use it independently,
which means we can just link one analog chip address to one hardware channel,
then users can access the mapped analog chip address by this hardware channel
triggered by hardware components instead of ADI software channels.

Thus we introduce one property named "sprd,hw-channels" to configure hardware
channels, the first value specifies the hardware channel id which is used to
transfer data triggered by hardware automatically, and the second value specifies
the analog chip address where user want to access by hardware components.

Since we have multi-subsystems will use unique ADI to access analog chip, when
one system is reading/writing data by ADI software channels, that should be under
one hardware spinlock protection to prevent other systems from reading/writing
data by ADI software channels at the same time, or two parallel routine of setting
ADI registers will make ADI controller registers chaos to lead incorrect results.
Then we need one hardware spinlock to synchronize between the multiple subsystems.

The new version ADI controller supplies multiple master channels for different
subsystem accessing, that means no need to add hardware spinlock to synchronize,
thus change the hardware spinlock support to be optional to keep backward
compatibility.

Required properties:
- compatible: Should be "sprd,sc9860-adi".
- reg: Offset and length of ADI-SPI controller register space.
- #address-cells: Number of cells required to define a chip select address
	on the ADI-SPI bus. Should be set to 1.
- #size-cells: Size of cells required to define a chip select address size
	on the ADI-SPI bus. Should be set to 0.

Optional properties:
- hwlocks: Reference to a phandle of a hwlock provider node.
- hwlock-names: Reference to hwlock name strings defined in the same order
	as the hwlocks, should be "adi".
- sprd,hw-channels: This is an array of channel values up to 49 channels.
	The first value specifies the hardware channel id which is used to
	transfer data triggered by hardware automatically, and the second
	value specifies the analog chip address where user want to access
	by hardware components.

SPI slave nodes must be children of the SPI controller node and can contain
properties described in Documentation/devicetree/bindings/spi/spi-bus.txt.

Example:
	adi_bus: spi@40030000 {
		compatible = "sprd,sc9860-adi";
		reg = <0 0x40030000 0 0x10000>;
		hwlocks = <&hwlock1 0>;
		hwlock-names = "adi";
		#address-cells = <1>;
		#size-cells = <0>;
		sprd,hw-channels = <30 0x8c20>;
	};