dt-bindings: irqchip: ti, sci-intr: Update bindings to drop the usage of gic as parent

Drop the firmware related dt-bindings and use the hardware specified
interrupt numbers within Interrupt Router. This ensures interrupt router
DT node need not assume any interrupt parent type.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200806074826.24607-5-lokeshvutla@ti.com