pci: add romsize property

This property can be useful for distros to set up known-good ROM sizes for
migration purposes.  The VM will fail to start if the ROM is too large,
and migration compatibility will not be broken if the ROM is too small.

Note that even though romsize is a uint32_t, it has to be between 1
(because empty ROM files are not accepted, and romsize must be greater
than the file) and 2^31 (because values above are not powers of two and
are rejected).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20201218182736.1634344-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210203131828.156467-3-pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: David Edmondson <david.edmondson@oracle.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>