livepatch: Export payload structure via livepatch_payload.h

livepatch: Export payload structure via livepatch_payload.h

The payload structure will be used by the new hooks implementation and
therefore its definition has to be exported via the livepatch_payload
header.
The new hooks will make use of the payload structure fields and the
hooks' pointers will also be defined in the payload structure, so
the structure along with all field definitions needs to be available
to the code being patched in.

Signed-off-by: Pawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: Andra-Irina Paraschiv <andraprs@amazon.com>
Reviewed-by: Eslam Elnikety <elnikety@amazon.de>
Reviewed-by: Leonard Foerster <foersleo@amazon.de>
Reviewed-by: Martin Pohlack <mpohlack@amazon.de>
Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>