PAM IPA for Spreadtrum platforms

Required properties:
- compatible: Should be "sprd,pam-ipa".
- reg: Specify the physical base address of the controller and length
  of memory mapped region.
- power-domains: Should be <&pd_ipa_sys>.
- vpower-supply: regulator for ipa_sys power
- syscons: Should contain the base address, offset and bit for each entry in "syscon-names".
- syscon-names: global register bits name, order and name should the same as code.
- sprd,cp-ul-intr-to-ap: cp ul common fifo interrupt to AP. 0: no, 1: yes
- sprd,cp-ul-threshold: cp ul common fifo threshold interrupt
- sprd,cp-ul-timeout: cp ul common fifo timeout interrupt
- sprd,cp-ul-flowctrl-mode: flow ctrl mode.
				0: rx fifo empty
				1: tx fifo full
				2: rx fifo empty & tx fifp full
- sprd,cp-ul-enter-flowctrl-watermark: enter flow ctrl watermark.
- sprd,cp-ul-exit-flowctrl-watermark: exit flow ctrl watermark.
- sprd,cp-dl-intr-to-ap: cp dl common fifo interrupt to AP. 0: no, 1: yes
- sprd,cp-dl-threshold: cp dl common fifo threshold interrupt
- sprd,cp-dl-timeout: cp dl common fifo timeout interrupt
- sprd,cp-dl-flowctrl-mode: flow ctrl mode.
				0: rx fifo empty
				1: tx fifo full
				2: rx fifo empty & tx fifp full
- sprd,cp-dl-enter-flowctrl-watermark: enter flow ctrl watermark.
- sprd,cp-dl-exit-flowctrl-watermark: exit flow ctrl watermark.

Examples:
	pam_ipa: pam-ipa@21140000 {
		compatible = "sprd,pam-ipa";
		reg = <0 0x21140000 0 0x100>;
		reg-names = "pam-ipa-base";
		power-domains = <&pd_ipa_sys>;
		vpower-supply = <&vddipa>;
		syscons = <&ipa_ahb_regs
			  REG_IPA_AHB_IPA_EB
			  MASK_IPA_AHB_PAM_IPA_EB>;
		syscon-names = "enable";

		sprd,cp-ul-intr-to-ap = <0>;
		sprd,cp-ul-threshold = <1>;
		sprd,cp-ul-timeout = <5>;
		sprd,cp-ul-flowctrl-mode = <1>;
		sprd,cp-ul-enter-flowctrl-watermark = <0x10>;
		sprd,cp-ul-exit-flowctrl-watermark = <0x04>;
		sprd,cp-dl-intr-to-ap = <0>;
		sprd,cp-dl-threshold = <0x10>;
		sprd,cp-dl-timeout = <0>;
		sprd,cp-dl-flowctrl-mode = <0>;
		sprd,cp-dl-enter-flowctrl-watermark = <0x24>;
		sprd,cp-dl-exit-flowctrl-watermark = <0x04>;
		sprd,pam-ipa-hw-ver = <1>;
		sprd,pam-ipa-hw-mode = <0>;
	};

