OMAP: powerdomain: split pwrdm_init() into two functions

In preparation for OMAP_CHIP() removal, split pwrdm_init() into three
functions.  This allows some of them to be called multiple times: for
example, pwrdm_register_pwrdms() can be called once to register
powerdomains that are common to a group of SoCs, and once to register
powerdomains that are specific to a single SoC.

The appropriate order to call these functions - which is enforced
by the code - is:

1. pwrdm_register_platform_funcs()
2. pwrdm_register_pwrdms() (can be called multiple times)
3. pwrdm_complete_init()

Convert the OMAP2, 3, and 4 powerdomain init code to use these new
functions.

While here, improve documentation, and increase CodingStyle
conformance by shortening some local variable names.

Signed-off-by: Paul Walmsley <paul@pwsan.com>

arch/arm/mach-omap2/powerdomain.h

@@ -162,7 +162,9 @@ struct pwrdm_ops {
 	int	(*pwrdm_wait_transition)(struct powerdomain *pwrdm);
 };
 
-void pwrdm_init(struct powerdomain **pwrdm_list, struct pwrdm_ops *custom_funcs);
+int pwrdm_register_platform_funcs(struct pwrdm_ops *custom_funcs);
+int pwrdm_register_pwrdms(struct powerdomain **pwrdm_list);
+int pwrdm_complete_init(void);
 
 struct powerdomain *pwrdm_lookup(const char *name);