powerpc/pseries: Move hcall_vphn() prototype into vphn.h

Consolidate the two prototypes for hcall_vphn() into vphn.h.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230823055317.751786-2-mpe@ellerman.id.au

powerpc/pseries: Move VPHN constants into vphn.h

These don't have any particularly good reason to belong in lppaca.h,
move them into their own header.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230823055317.751786-1-mpe@ellerman.id.au