powerpc/prom: Define structs for client architecture vectors

powerpc/prom: Define structs for client architecture vectors

The "client architecture vectors" are a series of structures we pass to
firmware to define various things, such as what processors we support
and many other options.

Each structure is entirely different so we have to define a different
struct for each one, but that's OK.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>