tools/libxl: Skip missing PCI GSIs

tools/libxl: Skip missing PCI GSIs

A PCI device may not have a legacy IRQ.  In that case, we don't need to
do anything, so don't fail in libxl__arch_hvm_map_gsi() and
libxl__arch_hvm_unmap_gsi().

Requires an updated pciback to return -ENOENT.

Fixes: f97f885c7198 ("tools: Add new function to do PIRQ (un)map on PVH dom0")
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>
master commit: d3ac8fdce26476d148fb2a8f18c7e5b0c153be0a
master date: 2025-03-13 10:23:52 +0100