based on Martins initial work

v3: fix ina2x9 calculations
v4: don't kmalloc(0), fix the lsb/pga stuff
v5: add a field to tell if the power reading may be invalid
    add nkvm_iccsense_read_all function
    check for the device on the i2c bus
Signed-off-by: Karol Herbst <nouveau@karolherbst.de>
Reviewed-by: Martin Peres <martin.peres@free.fr>