mfd: tps68470: Remove tps68470 MFD driver

This driver only covered one scenario in which ACPI devices with _HID
INT3472 are found, and its functionality has been taken over by the
intel-skl-int3472 module, so remove it.

Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Scally <djrscally@gmail.com>
Link: https://lore.kernel.org/r/20210603224007.120560-7-djrscally@gmail.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>