mfd: twl: Move header file out of I2C realm

include/linux/i2c is not for client devices. Move the header file to a
more appropriate location.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>