mfd: tqmx86: IO controller with I2C, Wachdog and GPIO

The QMX86 is a PLD present on some TQ-Systems ComExpress modules. It
provides 1 or 2 I2C bus masters, 8 GPIOs and a watchdog timer. Add an
MFD which will instantiate the individual drivers.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Lee Jones <lee.jones@linaro.org>