PBIAS internal regulator for SD card dual voltage i/o pads on OMAP SoCs.

Required properties:
- compatible:
  - should be "ti,pbias-dra7" for DRA7
  - should be "ti,pbias-omap2" for OMAP2
  - should be "ti,pbias-omap3" for OMAP3
  - should be "ti,pbias-omap4" for OMAP4
  - should be "ti,pbias-omap5" for OMAP5
  - "ti,pbias-omap" is deprecated
- reg: pbias register offset from syscon base and size of pbias register.
- syscon : phandle of the system control module
- regulator-name : should be
			pbias_mmc_omap2430 for OMAP2430, OMAP3 SoCs
			pbias_sim_omap3 for OMAP3 SoCs
			pbias_mmc_omap4 for OMAP4 SoCs
			pbias_mmc_omap5 for OMAP5 and DRA7 SoC

Optional properties:
- Any optional property defined in bindings/regulator/regulator.txt

Example:

		pbias_regulator: pbias_regulator {
			compatible = "ti,pbias-omap";
			reg = <0 0x4>;
			syscon = <&omap5_padconf_global>;
			pbias_mmc_reg: pbias_mmc_omap5 {
				regulator-name = "pbias_mmc_omap5";
				regulator-min-microvolt = <1800000>;
				regulator-max-microvolt = <3000000>;
			};
