ARM: OMAP5 / DRA7: PM: Avoid all SAR saves

Get rid of all assumptions about always having a sar base on *all*
OMAP4+ platforms. We dont need one on DRA7 and it is not necessary at
this point for OMAP5 either.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
[nm@ti.com: Split and optimize]
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>