Upgrading signal subscription logic.

Upgrading signal subscription logic.

Currently there is a common signal handler which receives signal
and then checks signal name to call signals handler function.

This process is done for every received signal.

If we register signals seperately then dbus will directly call
signal handler function.

Change-Id: Id3b641a19782da2163f1c3e5aebb63776738f849
Signed-off-by: Nishant Chaprana <n.chaprana@samsung.com>