platform/x86: asus-wmi: add support for showing middle fan RPM

Some newer ASUS ROG laptops now have a middle/center fan in addition
to the CPU and GPU fans. This new fan typically blows across the
heatpipes and VRMs betweent eh CPU and GPU.

This commit exposes that fan to PWM control plus showing RPM.

Signed-off-by: Luke D. Jones <luke@ljones.dev>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230630053552.976579-3-luke@ljones.dev


Signed-off-by: Hans de Goede <hdegoede@redhat.com>