staging: alarm-dev: Support to Compile as Module

Currently this alarm-dev can be compiles only as built in
driver. This adds support to compile it as module as well which is in
planned activity (See drivers/staging/android/TODO)

CC: Brian Swetland <swetland@google.com>
Signed-off-by: Pramod Gurav <pramod.gurav.etc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>