kerf: preserve PCI host bridge metadata

[nickolaev]

Kerf currently drops PCI host-bridge information when it parses and rewrites a
Multikernel device tree. As a result, a spawned kernel may receive its assigned
PCI device without the ECAM metadata needed to discover and access it.

This change:

• adds PCI host bridges to Kerf’s hardware model;
• parses the metadata from both DTB and DTS input;
• validates segments, bus ranges, ECAM alignment, and overlapping ranges; and
• preserves the metadata when generating an instance device tree.

Device trees without a pci-host-bridges section continue to work unchanged.

This complements the Linux SR-IOV assignment series, allowing the secondary
kernel to discover its assigned VF while the primary retains the PF.

Works alongside the relevant SR-IOV changes in the kernel multikernel/linux#4 .