docs: move pci-ids.txt to docs/specs/

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
reorganize pci-ids.txt

Some devices were missing, and we're using two PCI vendor ids.
This patch only adds devices that are already documented in hw/pci.h.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
virtio-9p: use symbolic constant, add to pci-ids.txt

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
ivshmem: use symbolic constant for PCI ID, add to pci-ids.txt

Due to disagreement on a name that is generic enough for hw/pci.h,
the symbolic constants are placed in the .c files.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
pci: use constants for devices under the 1B36 device ID, document them

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>