power: qpnp-qg: Add sleep-mode configuration for QG

Add support for updating the S2 state configuration
in sleep. This allows modifying the fifo-length, accumulator
interval and accumulator length when the device enters suspend.

Change-Id: I3e51dc34cea5c97a7f901d9981f908e35b8b0fb3
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>