power: qpnp-qg: Add logic to sanitize SDAM

Sanitize SDAM by writing a magic-number on
first boot and comparing the same on subsequent
reboots. This is to identify a SDAM corruption.

Change-Id: I12858a36dfa51886078f3c60b719ab34b9435f71
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>