drivers: Update the PMIC drivers for PM660

Bring in all the required PMIC drivers for SDM660 on 4.19 kernel
and make the required changes to successfully build these drivers.
Snapshot of the new drivers are added from the below commits
and required cleanup has been addressed :

From 4.14 kernel commit: 68b7015e5
qcom-rradc.c, qcom-tadc.c, qpnp-fg-gen3.c, qpnp-smb2.c,
qpnp-misc.c, smb1351-charger.c, qpnp-misc.h

From 4.9 kernel commit: ad779e060
smb-lib.c, smb-lib.h, smb-reg.h, smb138x-charger.c

qpnp-fg-gen3.c - additional changes from 4.9 pulled in.
smb-lib.c - additional changes from 4.14 pulled in.

Change-Id: I1c59dc0f41706fb10de82ff6bd6707758d351fd2
Signed-off-by: Shilpa Suresh <sbsure@codeaurora.org>