Revert "ti-st: add device tree support"

This reverts commit 46d0d333.

This binding is horrible and never should have been merged. It is not
documented nor are there any in tree users, so reverting it will not
break anything we care about. Lets revert it before we do have users.

The problems with it are:

- It is not documented.

- The GPIO connection is described with a custom property and uses Linux
GPIO numbering.

- The UART connection is described using the Linux tty device name.

Cc: Gigi Joseph <gigi.joseph@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>