input: Add initial support for TWL6040 vibrator

Add twl6040_vibra as a child of MFD device twl6040_codec. This
implementation covers the PCM-to-PWM mode of TWL6040 vibrator
module.

Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
CC: Tejun Heo <tj@kernel.org>
Acked-by: Dmitry Torokhov <dtor@mail.ru>