ARM: OMAP2+: Remove unused wakeup_cpu

After commit 32d174ed ("ARM: OMAP4: MPUSS PM: remove unnecessary
shim functions for powerdomain control") this is no longer used.

The code continues execution after context restore on the same CPU,
so we can just use pm_info->pwrdm.

Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Sebastian Reichel <sre@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Tony Lindgren <tony@atomide.com>