OMAP3: PM: Force write last pad config register into save area

Due to OMAP3 erratas 1.157, 1.185 the save of the last pad register
(ETK_D14 and ETK_D15) can fail sometimes when there is simultaneous
OCP access to the SCM register area. Fixed by writing the last
register to the save area.

Also, optimized the delay loop for the HW save to include an udelay(1),
which limits the number of unnecessary HW accesses to SCM register area
during the save.

Signed-off-by: Tero Kristo <tero.kristo@nokia.com>
Acked-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Anand Gadiyar <gadiyar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>