ARM: OMAP4: CPUidle: Avoid double idle driver registration

OMAP4 CPUidle driver registration call is under a loop which leads
to calling cpuidle_register_driver twice which is not intended.

Fix it by moving the driver registration outside the loop.

Reported-by: Nishanth Menon <nm@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>