xen/arm: IRQ: Replace {request, setup}_dt_irq by {request, setup}_irq

xen/arm: IRQ: Replace {request, setup}_dt_irq by {request, setup}_irq

Now that irq_desc stores the type of the IRQ (e.g level/edge,...), we don't
need to use specific IRQ function for ARM.

Also replace every call to dt_device_get_irq by platform_get_irq which is
a wrapper to this function and setup the IRQ type correctly.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Keir Fraser <keir@xen.org>