esoc: mdm-4x: Refactor implementation to separate out PON

Separate out Power handling logic of external modems.
Most external modems will differ only in how you power on,
warm reset, and cold reset the modem. The IPC logic can
be reused.

Change-Id: I9e5f16a5481a8aa9bfaf7e1482d50563354f661b
Signed-off-by: Hanumant Singh <hanumant@codeaurora.org>