Alphascale Clock Controller

The ACC (Alphascale Clock Controller) is responsible of choising proper
clock source, setting deviders and clock gates.

Required properties for the ACC node:
 - compatible: must be "alphascale,asm9260-clock-controller"
 - reg: must contain the ACC register base and size
 - #clock-cells : shall be set to 1.

Simple one-cell clock specifier format is used, where the only cell is used
as an index of the clock inside the provider.
It is encouraged to use dt-binding for clock index definitions. SoC specific
dt-binding should be included to the device tree descriptor. For example
Alphascale ASM9260:
#include <dt-bindings/clock/alphascale,asm9260.h>

This binding contains two types of clock providers:
 _AHB_ - AHB gate;
 _SYS_ - adjustable clock source. Not all peripheral have _SYS_ clock provider.
All clock specific details can be found in the SoC documentation.
CLKID_AHB_ROM		0
CLKID_AHB_RAM		1
CLKID_AHB_GPIO		2
CLKID_AHB_MAC		3
CLKID_AHB_EMI		4
CLKID_AHB_USB0		5
CLKID_AHB_USB1		6
CLKID_AHB_DMA0		7
CLKID_AHB_DMA1		8
CLKID_AHB_UART0		9
CLKID_AHB_UART1		10
CLKID_AHB_UART2		11
CLKID_AHB_UART3		12
CLKID_AHB_UART4		13
CLKID_AHB_UART5		14
CLKID_AHB_UART6		15
CLKID_AHB_UART7		16
CLKID_AHB_UART8		17
CLKID_AHB_UART9		18
CLKID_AHB_I2S0		19
CLKID_AHB_I2C0		20
CLKID_AHB_I2C1		21
CLKID_AHB_SSP0		22
CLKID_AHB_IOCONFIG	23
CLKID_AHB_WDT		24
CLKID_AHB_CAN0		25
CLKID_AHB_CAN1		26
CLKID_AHB_MPWM		27
CLKID_AHB_SPI0		28
CLKID_AHB_SPI1		29
CLKID_AHB_QEI		30
CLKID_AHB_QUADSPI0	31
CLKID_AHB_CAMIF		32
CLKID_AHB_LCDIF		33
CLKID_AHB_TIMER0	34
CLKID_AHB_TIMER1	35
CLKID_AHB_TIMER2	36
CLKID_AHB_TIMER3	37
CLKID_AHB_IRQ		38
CLKID_AHB_RTC		39
CLKID_AHB_NAND		40
CLKID_AHB_ADC0		41
CLKID_AHB_LED		42
CLKID_AHB_DAC0		43
CLKID_AHB_LCD		44
CLKID_AHB_I2S1		45
CLKID_AHB_MAC1		46

CLKID_SYS_CPU		47
CLKID_SYS_AHB		48
CLKID_SYS_I2S0M		49
CLKID_SYS_I2S0S		50
CLKID_SYS_I2S1M		51
CLKID_SYS_I2S1S		52
CLKID_SYS_UART0		53
CLKID_SYS_UART1		54
CLKID_SYS_UART2		55
CLKID_SYS_UART3		56
CLKID_SYS_UART4		56
CLKID_SYS_UART5		57
CLKID_SYS_UART6		58
CLKID_SYS_UART7		59
CLKID_SYS_UART8		60
CLKID_SYS_UART9		61
CLKID_SYS_SPI0		62
CLKID_SYS_SPI1		63
CLKID_SYS_QUADSPI	64
CLKID_SYS_SSP0		65
CLKID_SYS_NAND		66
CLKID_SYS_TRACE		67
CLKID_SYS_CAMM		68
CLKID_SYS_WDT		69
CLKID_SYS_CLKOUT	70
CLKID_SYS_MAC		71
CLKID_SYS_LCD		72
CLKID_SYS_ADCANA	73

Example of clock consumer with _SYS_ and _AHB_ sinks.
uart4: serial@80010000 {
	compatible = "alphascale,asm9260-uart";
	reg = <0x80010000 0x4000>;
	clocks = <&acc CLKID_SYS_UART4>, <&acc CLKID_AHB_UART4>;
	interrupts = <19>;
	status = "disabled";
};

Clock consumer with only one, _AHB_ sink.
timer0: timer@80088000 {
	compatible = "alphascale,asm9260-timer";
	reg = <0x80088000 0x4000>;
	clocks = <&acc CLKID_AHB_TIMER0>;
	interrupts = <29>;
};