hwmon: w83627ehf updates

Add control of fan minimum turn-on output levels, decoupling it from the
fan turn-off output level.  Add control of rate of change of fan output
level.  These in turn allow lower turn-off rotor speed and smoother
transitions for better thermal and acoustic control authority.  Add
support for constant fan speed and proportional-response operations modes.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: David Hubbard <david.c.hubbard@gmail.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>