powerpc/build: vdso linker warning for orphan sections

Add --orphan-handlin for vdsos, and adjust vdso linker scripts to deal
with orphan sections.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230609051002.3342-1-npiggin@gmail.com