OMAP2+: voltage: keep track of powerdomains in each voltagedomain

When a powerdomain is registered and it has an associated voltage domain,
add the powerdomain to the voltagedomain using voltdm_add_pwrdm().

Also add voltagedomain iterator helper functions to iterate over all
registered voltagedomains and all powerdomains associated with a
voltagedomain.

Modeled after a similar relationship between clockdomains and powerdomains.

Signed-off-by: Kevin Hilman <khilman@ti.com>
diff --git a/arch/arm/mach-omap2/powerdomain.h b/arch/arm/mach-omap2/powerdomain.h
index d8a7f91..42e6dd8 100644
--- a/arch/arm/mach-omap2/powerdomain.h
+++ b/arch/arm/mach-omap2/powerdomain.h
@@ -91,6 +91,7 @@
  * @pwrsts_mem_on: Possible memory bank pwrstates when pwrdm in ON
  * @pwrdm_clkdms: Clockdomains in this powerdomain
  * @node: list_head linking all powerdomains
+ * @voltdm_node: list_head linking all powerdomains in a voltagedomain
  * @state:
  * @state_counter:
  * @timer:
@@ -114,6 +115,7 @@
 	const u8 prcm_partition;
 	struct clockdomain *pwrdm_clkdms[PWRDM_MAX_CLKDMS];
 	struct list_head node;
+	struct list_head voltdm_node;
 	int state;
 	unsigned state_counter[PWRDM_MAX_PWRSTS];
 	unsigned ret_logic_off_counter;