serial: max3100: Remove custom HW shutdown support

serial: max3100: Remove custom HW shutdown support

While there is no user of this callback in the kernel, it also breaks
the relationship in the driver model. The correct implementation should
be done via GPIO or regulator framework.

Remove custom HW shutdown support for good and, if needed, we will
implement it correctly later on.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240402195306.269276-6-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>