counter: 104-quad-8: Remove IIO counter ABI

counter: 104-quad-8: Remove IIO counter ABI

The IIO counter driver has been superseded by the Counter subsystem as
discussed in [1]. This patch removes the IIO counter ABI from the
104-QUAD-8 driver.

[1] https://lore.kernel.org/lkml/20210119104105.000010df@Huawei.com/

Cc: Syed Nayyar Waris <syednwaris@gmail.com>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Link: https://lore.kernel.org/r/98a39983d5df761c058a469d1346fd8ffdef8516.1611973018.git.vilhelm.gray@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>