Phytium PWM controller

Required properties:
- compatible: should be "phytium,pwm"
- reg: physical base address and length of the controller's registers
- interrupts:  interrupt for the pwm controller
- clocks : clock specifiers for both ipg and per clocks.
- phytium,db: One or two <cntmod dutymod div updbcly dbpolarity> to describe dead-band configurations.
              "cntmod" indicates the counter mode (0 for modulo, 1 for up-and-down).
              "dutymod" indicdates which duty to compare with (0 for PMW_CCR, 1 for FIFO).
              "div" selects the clock divider value, from 0 to 1023.
              "updbcly" selects the rising edge delay cycles.
              "dbpolarity" selects the polarity for dead-band.

Example:

pwm0: pwm@2804a000 {
	compatible = "phytium,pwm";
	reg= <0x0 0x2804a000 0x0 0x1000>;
	interrupts = <GIC_SPI 173 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&sysclk_48mhz>;
	phytium,db = <0 0 0 1000 0>;
};