ARM: OMAP4+: CPUidle: Consolidate idle driver for OMAP5 support
The OMAP5 idle driver can re-use most of OMAP4 CPUidle driver
implementation. Also the next derivative SOCs are going to re-use
the MPUSS so, same driver with minor updates can be re-used.
Prepare the code so that its easier to add CPUidle support for
OMAP5 devices.