hwmon: add support for GMT G760A fan speed PWM controller

hwmon: add support for GMT G760A fan speed PWM controller

This controller can be found on the D-Link DNS-323 for instance, where
it is to be configured via static i2c_board_info in the board-specific
mach-orion/dns323-setup.c; this driver supports only the new-style
driver model.

Tested-by: Martin Michlmayr <[email protected]>
Signed-off-by: Herbert Valerio Riedel <[email protected]>
Signed-off-by: Matthew Palmer <[email protected]>
Signed-off-by: Laurie Bradshaw <[email protected]>
Signed-off-by: Martin Michlmayr <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>