ARM: OMAP4+: Move the CPU wakeup prepare code under smp_prepare_cpus()

Move the secondary CPU wakeup prepare code under smp_prepare_cpus() where it
belongs. It was remainder of the pen release code which was borrowed from
ARM code initially.

While at it drop the un-necessary sev() and barrier which was under
prepare code.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>