hwmon: (ibmpowernv) Add current(A) sensor

This patch exports current(A) sensors in inband sensors copied to
main memory by OCC.

Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>