ARM: shmobile: kzm9g: add AS3711 PMIC platform data

KZM9G uses an AS3711 PMIC to supply power to the CPU and the LCD backlight.
The PMIC on the board is pre-programmed to supply correct voltages to the
CPU, power supply to the backlight has to be turned on at run-time. The
latter is currently performed by a hard-coded I2C command sequence in the
board file. This patch removes the backlight hack and instead adds an I2C
device to instantiate the AS3711 MFD driver, which will add a regulator
device to dynamically adjust CPU voltages and a backlight device.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>