hwmon: xgene: Add support for X-Gene hwmon driver

[Itaru Kitayama]

Hi Hoan,

I've been testing your patch set on a Rev B0 system with ACPI, in dmesg
I see:

[    1.546444] xgene-slimpro-i2c APMC0D40:00: i2c mailbox channel 
request failed
[    1.570062] xgene-slimpro-hwmon APMC0D29:00: no pcc-channel property

what other packages or subsystems do we need to make this work on 
ACPI-based systems?

Itaru