drm/i915/hwmon: expose fan speed

drm/i915/hwmon: expose fan speed

Add hwmon support for fan1_input attribute, which will expose fan speed
in RPM. With this in place we can monitor fan speed using lm-sensors tool.

$ sensors
i915-pci-0300
Adapter: PCI adapter
in0:         653.00 mV
fan1:        3833 RPM
power1:           N/A  (max =  43.00 W)
energy1:      32.02 kJ

v2: Handle overflow, add mutex protection and ABI documentation
    Aesthetic adjustments (Riana)
v3: Change rotations data type, ABI date and version
v4: Fix wakeref leak
    Drop switch case and simplify hwm_fan_xx() (Andi)
v5: Rework time calculation, aesthetic adjustments (Andy)
v6: Drop redundant overflow logic (Andy)
    Split fan_input_read() into dedicated helper (Badal)
v7: Fix undefined reference to __udivdi3 for i386 (Andy)

Signed-off-by: Raag Jadav <raag.jadav@intel.com>
Reviewed-by: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240823034548.2670032-1-raag.jadav@intel.com