irqchip/ti-sci-inta: Do not store TISCI device id in platform device id field

Even though DT doesn't make active use of id field in platform_device, we cannot
hijack it to store TISCI device id. So create a field in struct ti_sci_inta
for storing TISCI id and drop usage of id field in platform_device.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200806074826.24607-10-lokeshvutla@ti.com