ARM: ux500: Apply a Device Tree node for the STMPE MFD

Here we apply the STMPE Multi-Functional Device's node to the
ST User Interface Board Device Tree file. It includes all of
the properties required for correct device initialsation.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>