hwmon: (ibmpowernv): Add support to read 64 bit sensors

The firmware has supported for reading sensor values of size u32.
This patch adds support to use newer firmware functions which allows
to read the sensors of size u64.

Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>