power: export guest channel header file

power: export guest channel header file

Adjust meson.build so that 'ninja install' copies the new header
file into the installation directory.

Fixes: 210c383e247b ("power: packet format for vm power management")
Fixes: cd0d5547e873 ("power: vm communication channels in guest")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Signed-off-by: David Hunt <david.hunt@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>