Pull regulator support code

This adds the support for the abstract regulator class interface which can be used to implement voltage/current regulators and generally control any device that has a fixed value range and the discrete number of steps

A regulator service can have a policy that only allows a limited subset of regulators to be accessed by the client service

Additionally, the TWL6030 voltage regulator support is implemented for the OMAP4 SoC.

Any suggestions are welcome. I think the policy part could be factored out in future because many drivers (GPIO, Clocks) seem to need a similiar resource-limiting capability.

--- an example of policy usage ---
```
	<start name="twl6030">
		<binary name="twl6030_regulator_drv"/>
		<resource name="RAM" quantum="1M" />
		<provides>
			<service name="Regulator"/>
		</provides>
		<config>
			<policy label="hwctl">
				<allowed_regulators>
					<VMMC/>
					<VAUX3/>
					<VUSIM/>
					<VCXIO/>
					<VDAC/>
					<CLK32KG/>
					<CLK32KAUDIO/>
				</allowed_regulators>
			</policy>
			<policy label="test-vreg-usb">
				<allowed_regulators>
					<VMMC/>
					<VUSB/>
				</allowed_regulators>
			</policy>
		</config>
		<route>
			<service name="LOG"> <child name="main_log"/> </service>
			<service name="I2C"> <child name="omap4_i2c1" /> </service>
			<any-service> <any-child/> <parent/> </any-service>
		</route>
	</start>
```