hwmon: (it87) Add support for IT8620E

IT8620E is mostly compatible to IT7828F. Add generic support for it.

IT8620E supports up to 6 fan tachometers and 6 pwm controls.
Support for the 6th tachometer and for the additional pwm controls
are addded in separate patches.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/it87

@@ -6,6 +6,10 @@ Supported chips:
     Prefix: 'it8603'
     Addresses scanned: from Super I/O config space (8 I/O ports)
     Datasheet: Not publicly available
+  * IT8620E
+    Prefix: 'it8620'
+    Addresses scanned: from Super I/O config space (8 I/O ports)
+    Datasheet: Not publicly available
   * IT8705F
     Prefix: 'it87'
     Addresses scanned: from Super I/O config space (8 I/O ports)
@@ -106,7 +110,7 @@ motherboard models.
 Description
 -----------
 
-This driver implements support for the IT8603E, IT8623E, IT8705F,
+This driver implements support for the IT8603E, IT8620E, IT8623E, IT8705F,
 IT8712F, IT8716F, IT8718F, IT8720F, IT8721F, IT8726F, IT8728F, IT8758E,
 IT8771E, IT8772E, IT8781F, IT8782F, IT8783E/F, IT8786E, IT8790E, and SiS950
 chips.
@@ -147,8 +151,11 @@ The IT8728F, IT8771E, and IT8772E are considered compatible with the IT8721F,
 until a datasheet becomes available (hopefully.)
 
 The IT8603E/IT8623E is a custom design, hardware monitoring part is similar to
-IT8728F. It only supports 16-bit fan mode, the full speed mode of the
-fan is not supported (value 0 of pwmX_enable).
+IT8728F. It only supports 3 fans, 16-bit fan mode, and the full speed mode
+of the fan is not supported (value 0 of pwmX_enable).
+
+The IT8620E is another custom design, hardware monitoring part is similar to
+IT8728F. It only supports 16-bit fan mode.
 
 The IT8790E supports up to 3 fans. 16-bit fan mode is always enabled.