mfd: Provide the STMPE driver with its own IRQ domain

The STMPE driver is yet another IRQ controller which requires its
own IRQ domain. So, we provide it with one.

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