gpio: stmpe: fix up interrupt enable logic

The STMPE driver assumes that the passed in IRQ type is
for rising or falling IRQs, not both, even though the
hardware actually supports this perfectly well. Likewise
the check for level IRQs is done against just high or low
level types, not for the case where it is combined with
other IRQs.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>