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

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

1. clkdm_register_platform_funcs()
2. clkdm_register_clkdms() (can be called multiple times)
3. clkdm_register_autodeps() (optional; deprecated)
4. clkdm_complete_init()

Convert the OMAP2, 3, and 4 clockdomain 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>