gpio: tegra186: Support multiple interrupts per bank

Tegra194 and later support more than a single interrupt per bank. This
is primarily useful for virtualization but can also be helpful for more
fine-grained CPU affinity control. To keep things simple for now, route
all pins to the first interrupt.

For backwards-compatibility, support old device trees that specify only
one interrupt per bank by counting the interrupts at probe time.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>