Add support for the touchscreen controllers provided by Wolfson
Microelectronics WM97xx series chips in both polled and streaming
modes.

These drivers have been maintained out of tree since 2003. During
that time the driver the primary maintainer was Liam Girdwood and
a number of people have made contributions including Dmitry Baryshkov,
Stanley Cai, Rodolfo Giometti, Russell King, Marc Kleine-Budde,
Ian Molton, Vincent Sanders, Andrew Zabolotny, Graeme Gregory,
Mike Arthur and myself. Apologies to anyone I have omitted.

Signed-off-by: Liam Girdwood <liam.girdwood@wolfsonmicro.com>
Signed-off-by: Graeme Gregory <gg@opensource.wolfsonmicro.com>
Signed-off-by: Mike Arthur <mike.arthur@wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>