i2c: client: added client factory.

Added a factory function for i2c_client's.

i2c_new_device:
	Create a new i2c_client for a device driver. Takes a pointer to
	a i2c_device_info structure as an argument. The i2c_device_info
	structure describes the layout of a chip using the I2C protocol.
	It includes a device name, end point address (I2C address), a
	bus (if not using the standard) and device file operations.

Signed-off-by: Michel Megens <dev@michelmegens.net>