regulator: fan53555: add regulator-initial-mode to set default mode

regulator: fan53555: add regulator-initial-mode to set default mode

regulator-initial-mode: default mode to set on startup
regulator-initial-mode is set as:
        REGULATOR_MODE_FAST                     0x1
        REGULATOR_MODE_NORMAL                   0x2
Example:
 vdd_cpu_b: syr827@40 {
                compatible = "silergy,syr827";
                reg = <0x40>;
                vin-supply = <&vcc5v0_sys>;
                regulator-compatible = "fan53555-reg";
                regulator-name = "vdd_cpu_b";
                regulator-min-microvolt = <712500>;
                regulator-max-microvolt = <1500000>;
                regulator-ramp-delay = <1000>;
                fcs,suspend-voltage-selector = <1>;
                regulator-always-on;
                regulator-boot-on;
                regulator-initial-state = <3>;
                regulator-initial-mode = <1>;/*1:pwm 2: auto mode*/
                        regulator-state-mem {
                        regulator-off-in-suspend;
                };
        };

Change-Id: I4d3bbd50fd40531113f2cc6fe63905e24888a752
Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>