ARM: dts: bcm2711: Add the BSC interrupt controller

The BSC controllers used for the HDMI DDC have an interrupt controller
shared between both instances. Let's add it to avoid polling.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/20210111142309.193441-1-maxime@cerno.tech