acpi/gpex: Create PCI link devices outside PCI root bridge

acpi/gpex: Create PCI link devices outside PCI root bridge

Currently, PCI link devices (PNP0C0F) are always created within the
scope of the PCI root bridge. However, RISC-V needs these link devices
to be created outside to ensure the probing order in the OS. This
matches the example given in the ACPI specification [1] as well. Hence,
create these link devices directly under _SB instead of under the PCI
root bridge.

To keep these link device names unique for multiple PCI bridges, change
the device name from GSIx to LXXY format where XX is the PCI bus number
and Y is the INTx.

GPEX is currently used by riscv, aarch64/virt and x86/microvm machines.
So, this change will alter the DSDT for those systems.

[1] - ACPI 5.1: 6.2.13.1 Example: Using _PRT to Describe PCI IRQ Routing

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Acked-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20240716144306.2432257-5-sunilvl@ventanamicro.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>