irqchip: Add Actions Semi Owl SIRQ controller

This interrupt controller is found in the Actions Semi Owl SoCs (S500,
S700 and S900) and provides support for handling up to 3 external
interrupt lines.

Each line can be independently configured as interrupt and triggers on
either of the edges or either of the levels. Additionally, each line
can also be masked individually.

Co-developed-by: Parthiban Nallathambi <pn@denx.de>
Co-developed-by: Saravanan Sekar <sravanhome@gmail.com>
Signed-off-by: Parthiban Nallathambi <pn@denx.de>
Signed-off-by: Saravanan Sekar <sravanhome@gmail.com>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1a010ef0eb78831b5657d74a0fcdef7a8efb2ec4.1600114378.git.cristian.ciocaltea@gmail.com