clockdomains: integrate OMAP3 clocks with clockdomain code

This patch integrates the OMAP3 clock tree with the clockdomain code.
This patch:

- marks OMAP34xx clocks with their corresponding clockdomain.

- adds code to convert the clockdomain name to a clockdomain pointer in the
  struct clk during clk_register().

- modifies OMAP2 clock usecounting to call into the clockdomain code
  when clocks are enabled or disabled.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>