ARM: OMAP2+: CM: determine CM base address from device tree

There is no need to provide the CM base address through a low-level API
from the low-level IO init, as this information is available through DT.
Re-routed the parsing function to be called from the CM drivers also to
simplify the implementation under io.c.

Signed-off-by: Tero Kristo <t-kristo@ti.com>