davinci: cpuidle: move mapping of DDR2 controller registers out of driver

When suspend is supported, both cpuidle and suspend code
need to work on DDR2 registers. Instead of mapping the
DDR2 registers twice, do it once outside of cpuidle
driver and let cpuidle driver get the virtual base address
of DDR2 registers.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>