soc: arm64: qemu: bump highest IRQ when ITS is enabled

The purpose of the GIC ITS is to translate message-passing interrupts into
LPIs. The LPI range starts at value 8192, which means the current default
value (200) is too low. Therefore, bump the highest IRQ number when ITS
is enabled.

Signed-off-by: Rodrigo Cataldo <rodrigo.cataldo@huawei.com>
Co-authored-by: Henri Xavier <datacomos@huawei.com>