platform: qpnp-power-on: Add support for TWM config

TWM (traditional watch mode) is a low-power mode
configuration on the BG platform. Add a notification
callback to be notified of an entry into this mode.

Add logic to skip the PS_HOLD reset configuration and
initiate the PBS trigger if TWM mode is enabled.
The PBS trigger configures the PMIC for TWM entry.

Change-Id: I31a48c8d2506a668b18737ec3da827cff27b830d
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>