ARM: OMAP4+/AM33xx: CM: add common API for cm_wait_module_idle

Adds a generic CM driver API for waiting module to enter idle / standby.
The SoC specific implementations are registered through cm_ll_data.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Paul Walmsley <paul@pwsan.com>
Tested-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>