power: batter-charger-gauge: add API for reading battery current

power: batter-charger-gauge: add API for reading battery current

Add API for reading battery current throuch IIO channels.
IIO channel information is read from battery gauge device node.

bug 1413219

Change-Id: I87094acbd15796a16acb520ba52c2351439e4bbb
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reviewed-on: http://git-master/r/395550
(cherry picked from commit ff66b38933844c9cd6b57abcf3073b13a35dc092)
Reviewed-on: http://git-master/r/395782
GVS: Gerrit_Virtual_Submit
Reviewed-by: Venkat Reddy Talla <vreddytalla@nvidia.com>
Tested-by: Venkat Reddy Talla <vreddytalla@nvidia.com>