ARM: OMAP5 / DRA7: PM: Update CPU context register offset

On OMAP5, RM_CPUi_CPUi_CONTEXT offset has changed. Update the code
so that same code works for OMAP4+ devices. DRA7 and OMAP5 have the same
context offset as well.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
[rnayak@ti.com: for DRA7]
Signed-off-by: Rajendra Nayak <rnayak@ti.com>
[nm@ti.com: rebase, split/merge etc..]
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>