staging: alarm-dev: Refactor alarm-dev ioctl code in prep for compat_ioctl

Cleanup the Android alarm-dev driver's ioctl code to refactor it
in preparation for compat_ioctl support.

Cc: Serban Constantinescu <serban.constantinescu@arm.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Colin Cross <ccross@google.com>
Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>