ARM: OMAP2+: control: add syscon support for register accesses

Control module driver needs to support syscon for register accesses, as
the DT hierarchy for control module driver is going to be changed. All
the control module related features will be moved under control module
node, including clocks, pinctrl, and generic configuration register
access. Temporary iomap is still provided very early in the boot for
access while syscon is not yet ready.

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