emulation: qemu-sbsa: Fill in correct ITS ID

emulation: qemu-sbsa: Fill in correct ITS ID

The ACPI IORT and ACPI MADT needs to use the same IDs when referencing
GIC ITS. The GIC-v3 ITS driver uses dev_seq(dev) to generate a unique ID
for the MADT, but qemu sbsa-ref hardcodes it.
Currently it's not the same ID, breaking interrupt routing on the OS.

Don't assume it's 0 and fetch it from the device instead.

TEST: Fixes non working IRQs in QEMU sbsa-ref.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>