ARM: 7874/2: bL_switcher: Remove cpu_hotplug_driver_{lock,unlock}()

Commit 6dedcca610c6 ("hotplug, powerpc, x86: Remove
cpu_hotplug_driver_lock())" removes the the definition of
cpu_hotplug_driver_{lock,unlock} APIs, thereby causing a build error.

Replace these calls with {lock,unlock}_device_hotplug().

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>