power: qpnp-fg-gen4: add support to register with thermal core framework

Add support to register FG driver to register with thermal core
framework so that the battery temperature can be monitored by any
thermal governor and userspace is one of them.

Change-Id: Ib828474cf464d78be4bf843b6b59a6adabe005cf
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>