power: qpnp-smb2: Update the GEN3 fuel gauge driver

Update the GEN3 fuel gauge driver to make it compatible with
the msm-3.18 kernel. The following are the updates -

1. Support the legacy SPMI driver interface
2. Add interrupts flags

CRs-Fixed: 2076000
Change-Id: I3a14d8f6810efa5eac5cb3a744811913b4949e94
Signed-off-by: Ankit Sharma <ansharma@codeaurora.org>
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>