ARM: OMAP2/3: CM: make cm_split_idlest_reg SoC calls static

CM driver has a generic API which calls the SoC specific split function
through cm_ll_data, so there is no need for the SoC specific functions to
be publicly available.

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