Staging: mrst_touchscreen - clean up input side

Fix most of the stuff that Dmitry pointed out. This leaves the mutex in IRQ
and misuse of SPI to sort out.

Also fix the build bits so it actually builds in staging - whoops.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>