Do not explicity disconnect Data during power down for 1x.

In 1x, if the data call is torn down before radio power off, modem will
have to send a data call release and change to initialization state followed
by idle state and send out power down registration. If the power off request is sent
to the modem during Initialization state after call release, there is a chance that
modem does not perform power down registration.

Instead if we directly initiate a power down, modem just sets a power down registration
bit in the release order. This change also optimizes the power down procedure in 1x by
letting the modem handle data call release during power down.

Change-Id: I0f083cc3b005ec1e64105350abb43d10583b0881