ARM: OMAP4: CM: make cminst direct register access functions static

These shall not be accessed outside the CM driver. This also removes the
need for the cminst44xx.h header.

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>