qemu: Introduce qemuDomainHostdevPrivatePtr

qemu: Introduce qemuDomainHostdevPrivatePtr

Modeled after the qemuDomainDiskPrivatePtr logic, create a privateData
pointer in the _virDomainHostdevDef to allow storage of private data
for a hypervisor in order to at least temporarily store auth/secrets
data for usage during qemuBuildCommandLine.

NB: Since the qemu_parse_command (qemuParseCommandLine) code is not
expecting to restore the auth/secret data, there's no need to add
code to handle this new structure there.

Updated copyrights for modules touched. Some didn't have updates in a
couple years even though changes have been made.

Signed-off-by: John Ferlan <jferlan@redhat.com>