OMAP2+: voltage: start towards a new voltagedomain layer

Start cleaning up the voltage layer to have a voltage domain layer
that resembles the structure of the existing clock and power domain
layers.  To that end:

- move the 'struct voltagedomain' out of 'struct omap_vdd_info' to
  become the primary data structure.

- convert any functions taking a pointer to struct omap_vdd_info into
  functions taking a struct voltagedomain pointer.

- convert the register & initialize of voltage domains to look like
  that of powerdomains

- convert omap_voltage_domain_lookup() to voltdm_lookup(), modeled
  after the current powerdomain and clockdomain lookup functions.

- omap_voltage_late_init(): only configure VDD info when
  the vdd_info struct is non-NULL

Signed-off-by: Kevin Hilman <khilman@ti.com>

arch/arm/mach-omap2/pm.c

@@ -181,7 +181,7 @@ static int __init omap2_set_init_voltage(char *vdd_name, char *clk_name,
 		goto exit;
 	}
 
-	voltdm = omap_voltage_domain_lookup(vdd_name);
+	voltdm = voltdm_lookup(vdd_name);
 	if (IS_ERR(voltdm)) {
 		printk(KERN_ERR "%s: Unable to get vdd pointer for vdd_%s\n",
 			__func__, vdd_name);