clk: stm32f7: add clock driver for stm32f7 family

add basic clock driver support for stm32f7 to enable clocks required by
the peripherals.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

doc/device-tree-bindings/clock/st,stm32-rcc.txt

@@ -0,0 +1,95 @@
+STMicroelectronics STM32 Reset and Clock Controller
+===================================================
+
+The RCC IP is both a reset and a clock controller.
+
+Please refer to clock-bindings.txt for common clock controller binding usage.
+Please also refer to reset.txt for common reset controller binding usage.
+
+Required properties:
+- compatible: Should be:
+  "st,stm32f42xx-rcc"
+  "st,stm32f469-rcc"
+- reg: should be register base and length as documented in the
+  datasheet
+- #reset-cells: 1, see below
+- #clock-cells: 2, device nodes should specify the clock in their "clocks"
+  property, containing a phandle to the clock device node, an index selecting
+  between gated clocks and other clocks and an index specifying the clock to
+  use.
+
+Example:
+
+	rcc: rcc@40023800 {
+		#reset-cells = <1>;
+		#clock-cells = <2>
+		compatible = "st,stm32f42xx-rcc", "st,stm32-rcc";
+		reg = <0x40023800 0x400>;
+	};
+
+Specifying gated clocks
+=======================
+
+The primary index must be set to 0.
+
+The secondary index is the bit number within the RCC register bank, starting
+from the first RCC clock enable register (RCC_AHB1ENR, address offset 0x30).
+
+It is calculated as: index = register_offset / 4 * 32 + bit_offset.
+Where bit_offset is the bit offset within the register (LSB is 0, MSB is 31).
+
+To simplify the usage and to share bit definition with the reset and clock
+drivers of the RCC IP, macros are available to generate the index in
+human-readble format.
+
+For STM32F4 series, the macro are available here:
+ - include/dt-bindings/mfd/stm32f4-rcc.h
+
+Example:
+
+	/* Gated clock, AHB1 bit 0 (GPIOA) */
+	... {
+		clocks = <&rcc 0 STM32F4_AHB1_CLOCK(GPIOA)>
+	};
+
+	/* Gated clock, AHB2 bit 4 (CRYP) */
+	... {
+		clocks = <&rcc 0 STM32F4_AHB2_CLOCK(CRYP)>
+	};
+
+Specifying other clocks
+=======================
+
+The primary index must be set to 1.
+
+The secondary index is bound with the following magic numbers:
+
+	0	SYSTICK
+	1	FCLK
+
+Example:
+
+	/* Misc clock, FCLK */
+	... {
+		clocks = <&rcc 1 STM32F4_APB1_CLOCK(TIM2)>
+	};
+
+
+Specifying softreset control of devices
+=======================================
+
+Device nodes should specify the reset channel required in their "resets"
+property, containing a phandle to the reset device node and an index specifying
+which channel to use.
+The index is the bit number within the RCC registers bank, starting from RCC
+base address.
+It is calculated as: index = register_offset / 4 * 32 + bit_offset.
+Where bit_offset is the bit offset within the register.
+For example, for CRC reset:
+  crc = AHB1RSTR_offset / 4 * 32 + CRCRST_bit_offset = 0x10 / 4 * 32 + 12 = 140
+
+example:
+
+	timer2 {
+		resets	= <&rcc STM32F4_APB1_RESET(TIM2)>;
+	};