ARM: OMAP: Mistral board updates (spi, ...)

This adds the OSK/Mistral specific glue for the omap_uwire driver and
its ADS 7846 touchscreen.  It also moves the lcd and keypad setup so
it's grouped with the other Mistral-specific setup code, and provides
comments about which switch maps to which reported key.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>