platform/x86: system76_acpi: Report temperature and fan speed

platform/x86: system76_acpi: Report temperature and fan speed

Add a hwmon interface to report CPU/GPU temperature and fan speed.
sensors now reports an ACPI interface with the entries:

system76_acpi-acpi-0
Adapter: ACPI interface
CPU fan:        0 RPM
GPU fan:        0 RPM
CPU temp:     +47.0°C
GPU temp:      +0.0°C

Signed-off-by: Jeremy Soller <jeremy@system76.com>
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Link: https://lore.kernel.org/r/20211006202202.7479-2-tcrawford@system76.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>