Add support for ILI251x touch controller. This controller is similar
to the ILI210x, except for the following differences:
- Does not support I2C R-W transfer, Read must be followed by an
  obscenely long delay, and then followed by Write
- Does support 10 simultaneous touch inputs.
- Touch data format is slightly different, pressure reporting does not
  work although the touch data contain such information.
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>