sh: enable sparseirq for highlander and r2d.

highlander and r2d are the only remaining ones that were blocking
sparseirq being turned on by default, but it turns out that they already
work fine with it by virtue of register_intc_controller(). As such, we
can kill off the dependencies and turn it on by default.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>