Binding for TZ1090 Top level register clocks.

This binding uses the common clock binding[1]. It represents the clocks
controlled from the top level registers of the TZ1090, and encompasses most of
the complexity of the TZ1090 clock tree:

[1] Documentation/devicetree/bindings/clock/clock-bindings.txt

Required properties:
- compatible         : Shall be "img,tz1090-top-cr", "syscon".
- #clock-cells       : From common clock binding; shall be set to 1.
- reg                : Base address for clock registers in top level register
                       region.
- clocks             : Clock specifiers for each input clock.
- clock-names        : Labels for each input clock specified in clocks.
                       Can contain the following entries:
                       "xtal1"        : XTAL1 oscillator.
                       "xtal3"        : XTAL2 oscillator.
                       "ext_adc_dac"  : External ADC/DAC clock input.
                       "ddr_en"       : Output of HEP DDR clock gate.
                       "afe_progdiv1",
                       "afe_progdiv3",
                       "afe_rxsync",
                       "afe_txsync",
                       "iqadc_sync"   : Output clocks from AFE block.

Optional properties:
- clock-indices      : From common clock binding. Allows clock-output-names to
                       be sparse.
- clock-output-names : From common clock binding. May be used to name specific
                       output clocks so that other clock providers can find
                       the clocks by name before the provider has been
                       instantiated. Can contain:
                       "sys", "sys_x2_undeleted" "scb", "ext_stc0", "ext_stc1",
                       "if1", "if0", "sys_ucc1", "sys_mtx", "meta", "ucc0",
                       "ucc1_del", "sys_undeleted", "afe", "adcpll_div", "uart",
                       "pdm", "spi0", "spi1", "i2sm", "usb_phy", "sdhost",
                       "ring_osc", "i2s", "meta_trace", "pixel", "out0", "out1",
                       "ddr", "sys_pll", "sys_pdc"

Clock Specifier Definition:
- <1st-cell>: Output clock number. Use constants from
              <dt-bindings/clock/tz1090-top.h>.

Examples:
	top_cr: top_cr {
		compatible = "img,tz1090-top-cr", "syscon";
		#clock-cells = <1>;
		reg = <0x02005900 0xb0>;
		/* input clocks */
		clocks = <&xtal1>, <&xtal2>, <&ext_adc_dac>,
			 <&hep_cr CLK_HEP_DDR_EN>;
		clock-names = "xtal1", "xtal2", "ext_adc_dac",
			      "ddr_en";
		/* output clocks for other clock providers */
		clock-indices = <CLK_TOP_SYS>,
				<CLK_TOP_SYS_X2_UNDELETED>;
		clock-output-names = "sys",
				     "sys_x2_undeleted";
	};

	ir {
		...
		clocks = <&pdc_cr CLK_PDC_32KHZ>,
			 <&top_cr CLK_TOP_PDC>;
		clock-names = "core", "sys";
		...
	};