xen: arm: Assume level triggered means high, not low.

xen: arm: Assume level triggered means high, not low.

When reading back the ICFG register we cannot know the polarity of the
configuration, just that it is level or edge.

Since falling edge and low level are invalid for SPIs we should assume
rising edge and high level (we have no better information for PPIs, so
it'll have to do).

We already assumed rising edge, switch to high level as well.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Julien Grall <julien.grall@linaro.org>