clk: Add support for fundamental zynq clks

Provide simplified models for the necessary clocks on the zynq-7000
platform.  Currently, the PLLs, the CPU clock network, and the basic
peripheral clock networks (for SDIO, SMC, SPI, QSPI, UART) are modelled.

OF bindings are also provided and documented.

Signed-off-by: Josh Cartwright <josh.cartwright@ni.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Acked-by: Michal Simek <michal.simek@xilinx.com>

Documentation/devicetree/bindings/clock/zynq-7000.txt

@@ -0,0 +1,55 @@
+Device Tree Clock bindings for the Zynq 7000 EPP
+
+The Zynq EPP has several different clk providers, each with there own bindings.
+The purpose of this document is to document their usage.
+
+See clock_bindings.txt for more information on the generic clock bindings.
+See Chapter 25 of Zynq TRM for more information about Zynq clocks.
+
+== PLLs ==
+
+Used to describe the ARM_PLL, DDR_PLL, and IO_PLL.
+
+Required properties:
+- #clock-cells : shall be 0 (only one clock is output from this node)
+- compatible : "xlnx,zynq-pll"
+- reg : pair of u32 values, which are the address offsets within the SLCR
+        of the relevant PLL_CTRL register and PLL_CFG register respectively
+- clocks : phandle for parent clock.  should be the phandle for ps_clk
+
+Optional properties:
+- clock-output-names : name of the output clock
+
+Example:
+	armpll: armpll {
+		#clock-cells = <0>;
+		compatible = "xlnx,zynq-pll";
+		clocks = <&ps_clk>;
+		reg = <0x100 0x110>;
+		clock-output-names = "armpll";
+	};
+
+== Peripheral clocks ==
+
+Describes clock node for the SDIO, SMC, SPI, QSPI, and UART clocks.
+
+Required properties:
+- #clock-cells : shall be 1
+- compatible : "xlnx,zynq-periph-clock"
+- reg : a single u32 value, describing the offset within the SLCR where
+        the CLK_CTRL register is found for this peripheral
+- clocks : phandle for parent clocks.  should hold phandles for
+           the IO_PLL, ARM_PLL, and DDR_PLL in order
+- clock-output-names : names of the output clock(s).  For peripherals that have
+                       two output clocks (for example, the UART), two clocks
+                       should be listed.
+
+Example:
+	uart_clk: uart_clk {
+		#clock-cells = <1>;
+		compatible = "xlnx,zynq-periph-clock";
+		clocks = <&iopll &armpll &ddrpll>;
+		reg = <0x154>;
+		clock-output-names = "uart0_ref_clk",
+				     "uart1_ref_clk";
+	};